Ebike Battery Pack Energy Density Talk

[emtbeast]

Hello ebike community.

I am seeing a lot of talk out there about new battery tech, high energy density etc...and it's giving me a bit of a headache seeing how easy it is for brands to wash people's minds with some easy marketing bs.

I'm opening this thread for talk about new ebike energy pack tech improvements on energy density and similar.

I will take the newer 800Wh packs, as those are the ones recently a lot of talk is about high energy density without any real or lack of explanation why so.

It will be a bit lengthy post so Let's dig in...

Shortly said, currently there is no new market available new magic battery tech going on at any brands packs period! For example the so called "new tech" has been already out there for at least 2 years(Giant 800Wh pack).

All 36V 800Wh battery packs out there use the industry standard high capacity 21700(21mm x 70mm) 3,6V 5,5Ah cells.

Maybe someone will correct me, so a note here: the cells in the Giant 800Wh packs are actually not industry standard as they are made exclusively for Giant by Panasonic and are a 22700(22mm x 71mm) cells, so slightly thicker and so have a slightly higher capacity of 5,65Ah and so slightly superior in some factors to other industry standard 21700 cells as larger cells bring increased energy density per cell, the battery heats up less, due to a slightly higher capacity it can operate in the optimal SOC window for longer and its lifetime is so extended. At this point we could go into cell chemistry etc, but for the low current draw of electric motors on ebikes that's basically an irrelevant factor.

All 36V system 800Wh ebike battery packs use 40 cells in a 10S4P electrical configuration(10 cells connected in series = 10 x 3,6V = 36V) and 4 series groups connected in parallel. It physically can't be done any other way because you need 10 cells connected in series to get 36V needed for the system. When you reduce the parallel connected series groups the lower the capacity of the pack and also smaller and lighter the pack, i. e. 600Wh with a 10S3P configuration with 30 cells.

Informational notes:
1. The cells when fully charged have a voltage of cca 4,2V(the whole pack 42V), when discharged fully the cell voltage drops to a minimum limit of cca 2,5V(the whole pack 25V).

2. As the motor is rated at 36V by specs, once the battery pack voltage when discharging starts falling under 36V, a rider starts to feel decreased system power, faster discharging of the pack or in other words the so called battery sag.

Going further, the only difference between different 800Wh packs is how the 40 cells are stacked inside the housing, the used BMS and cell holder material, hence the housing dimensions.

The Dji 800Wh(dimensions of 561mm x 71mm x 49mm) looking from one side the cells are most likely stacked in a 7(length) x 3(width) x2(height) configuration. That configuration leaves cca 6cm x 5cm room for the BMS, the connector and wiring. The configuration internally takes about 70mm in width and 45mm in height(including cell holders), looking at the dimensions of the pack that means the housing walls are cca 2mm - 2,2mm thick.

The new Bosch 800Wh(dimensions of 424mm x 77mm x 71mm) most probably has the cells stacked in 5(length) x 3(width) x3(height) configuration. This configuration ensures a lower and closer to the middle of the bike center of gravity especially if the empty space for the BMS is placed at the top of the pack.

So we have tradeoff here:
Dji - lower weight/higher out placed center of gravity
Bosch - higher weight/lower and more mid placed center of gravity

Battery cell weights:
A typical 21700 cell weighs cca 65g.
As there are no weight specs for the 22700 cells, doing some simple reverse math magic brings us to 68g. Corrected, two years ago when I was looking for info on the 22700 cells there were none as the they were brand new. I did a check up and found some info on them so the weight is cca 75g per cell, the capacity is cca 5,65Ah as predicted by my calculations. I corrected all the other Giant calculations accordingly.

40 x 21700 cell x 65g = 2,6kg
40 x 22700 cell x 75g = 3,0kg

Weight comparison of three 800Wh packs 》

The Dji 800wh pack is cca 3,74kg.
So the housing with the rest of the internals(BMS, wiring, connector, cell holders,...) is cca 1,14kg.

The new Bosch 800Wh is cca 3,9kg.
So the housing with the rest of the internals(BMS, wiring, connector, cell holders,...) is cca 1,3kg.

The Giant 800Wh is cca 4,3kg.
So the housing with the rest of the internals(BMS,wiring, connector, cell holders,...) is cca 1,3kg.

The most weight savings at current ebike batterys come from the housing material choice, it's thickness, implementation and safety standards manufacturers choose to use, the highest being the EN50604 (safety standard for lithium batteries for LEV - Light Electric Vehicles). Some manufacturers(i. e. Giant) go for highest safety standards(increase weight), other's use lower standards(lower weight).
All used standards must still ensure appropriate levels of safety prescribe by each countrys regulatory institutions.

Some thoughts on: how to get the battery weight down more - enter specific material density:

For this I'm not 100% sure(there is no spec data on battery housing materials) but I'm pretty sure most manufacturers use aluminum or PETE/PVC.

Different material densitys:
2,7g/cm³ ALUMINUM
2,2g/cm³ CARBON = (Alu - 18%)
1,7g/cm³ MAGNESIUM = (Alu - 37%)
1,2g/cm³ PETE/PVC = (Alu - 55%)

An Example:
The Giant 800Wh pack weighs cca 4,3kg. As already pointed out up the housing is made out of aluminum and weighs 1,3kg(with internals).
For this example let's say 0,3kg are the internals. So we have 1,0kg of pure aluminum housing. If this housing was made of magnesium we can deduct 37% of weight as the specific density of magnesium is 37% lower than aluminum.

1,0kg - 37% = 0,63kg

At a 0,4kg difference it would mean a Giant 800Wh pack with a magnesium housing would weigh 3,9kg.

Other examples:
A Dji 800Wh pack with a magnesium housing would weigh cca 0,4kg less about 3,3 kg

A Bosch 800Wh pack with a magnesium housing would weigh cca 0,5kg less about 3,4kg

Of course there is the cost aspect, but IMO as the amount of material used for each battery is minimal it shouldn't affect the price per pack for the end consumer to much as:

1kg of aluminum is 2,6€.
1kg of magnesium is 5,9€.

Aluminum housing:
1,4kg x 2,6€/kg = 3,64€

Magnesium housing:
0,88kg x 5,9€/kg = 5,20€

But of course as usual in todays world the manufacturers would market the bs out of a new lightweight magnesium battery housing and skyrocket the prices for the end consumers...

Another way to further decrease weight would be using thiner thus lighter housing walls shaped in a way that increases structural rigidity(i. e. wave, zigzag, pattern - already used by some manufacturers in a mild form).

Most probably it's the cost of manufacturing and the cost/availability of material why magnesium isn't used for the mentioned application. Maybe someone from the actual industry can elaborate further.

Efficiency and energy density of batterys due to the housing materials:
Some manufacturers use plastic materials for their batterys to reduce weight, while this is great for high weight savings it's not so great from safety concerns and heat dissipation reasons. A metal housing dissipates heat much better and so aids to increased efficiency.

To conclude, a higer ebike battery energy density does not come from some special new magical cells or battery technology like a lot of talk about it is out there, but from plain simple housing material choice, it's implementation and the chosen safety standards.

IMO the breakthrough however will come when a first manufacturer uses an industry standard solid state battery specialy made for ebikes, that will drastically lower the weight at the same or even higher capacity rates. Current best ebike battery energy densitys hover around 200Wh/kg. A solid state battery could raise that to a realistic 300Wh/kg.
That would mean we could have a 600Wh pack at 2kg or 900Wh pack at 3kg. I know the form factor is a question here and we are still probably far away from a market ready product, but I am sure if an average Joe(here) is thinking about it, somewhere out there is a company thinking the same or maybe it's already in the r&d stage.

Going of topic a bit for the end, a high battery energy density isn't everything, especially not on an emtb, as previously mentioned IMO by lowering the center of gravity, more emphasis is placed on making the ride more enjoyable and efficient especially on emtbs ...while ensuring the same specs as the competition, that's what really counts at an emtb development. I have a feeling that only a few brands go so deep at development, but usually those bring out a ride that is amazing on the trails.

Hope all this makes some sense and helps clear up things about energy density and maybe get a good discussion down the road.

 

[Doomanic]

Not all battery housings are aluminium though. Canyon's infamous cracking pack looks to be plastic.

 

[knut7]

We might have a different view of what's new battery tech and not. The 5.56Ah 22700 cells used by the giant has a similar energy density to the 5Ah 21700 that has been the standard for years.

What's new with the Giant 400 Wh battery on the lightweight Trance?

It seems Giant forgot about emtbforums for the launch of the new and lightweight Trance X Advanced E+ Elite. Which I think is sad. At least it saved me the stress of figuring out how to fit such a long name into a headline. Much has been said...

www.emtbforums.com

I assumed Bosch used the same cells, but when I spoke to Bosch late this year, they confirmed they use a different cell. The 400 Wh Compacttube battery pack launched in 2023 use 5.56Ah 21700 cells. I'd say this is new battery tech as it's 0.56 Ah more than the 210700 cells used up untill then, with comparable weight.

When Sram launched their motor in 2023, they introduced a 630 Wh batterypack using 21700 cells. We asked them to confirm it was 21700 cells as these battery packs were built using 18650 cells up untill then. To acheive this, they need 5.8 Ah cells. This was the first time I saw a battery with these cells, so I'd call them new battery tech.

You provide a bit of info here that I'm not sure is correct. The old 5 Ah cells are close to 70 g, claimed weight for the Samsung 50E 21700 5 Ah is 68.7g. The LG M58T is about 3g heavier than the Panasonic 5Ah cell, at 71.7g. INR21700-M58T

I don't think the cells are discharged as low as 2.5 V for this application. And most battery packs should have no problem delivering all the current a full-power motor can draw at well below 50% soc (36V). It requires about 20 A to deliver 700 W at 36 V. That's ~5 A drawn from each cell for a 10s4p pack, well below the rated max discharge of 10.8A for the M58T. You need low cell temperature and/or even lower charge before the cells are pushed to their limit. The new 600-630 Wh battery packs will be asked to deliver 6.5 Ah to get 700 W at 36 V, that should still be fine. The 10s2p configuration will struggle though, and it's used with the 600 W Bosch SX motor. Bosch says it's fine as this motor will only peak at 600 W, riders aren't able to draw 600 W constinous riding the SX motor. But using the CX motor with the 400 Wh battery and the motor might start derating at 80% SOC, as this motor can have a more prolonged 600W output.

 

[oettam20]

Thank you for these interesting notes! May I ask about your background? Do you work in the industry?

 

[RichMorr]

What about a 48v motor system like the specialzed SL and fazua ride 60 motor.?

 

[emtbeast]

We might have a different view of what's new battery tech and not. The 5.56Ah 22700 cells used by the giant has a similar energy density to the 5Ah 21700 that has been the standard for years.

What's new with the Giant 400 Wh battery on the lightweight Trance?

It seems Giant forgot about emtbforums for the launch of the new and lightweight Trance X Advanced E+ Elite. Which I think is sad. At least it saved me the stress of figuring out how to fit such a long name into a headline. Much has been said...

www.emtbforums.com

I assumed Bosch used the same cells, but when I spoke to Bosch late this year, they confirmed they use a different cell. The 400 Wh Compacttube battery pack launched in 2023 use 5.56Ah 21700 cells. I'd say this is new battery tech as it's 0.56 Ah more than the 210700 cells used up untill then, with comparable weight.

When Sram launched their motor in 2023, they introduced a 630 Wh batterypack using 21700 cells. We asked them to confirm it was 21700 cells as these battery packs were built using 18650 cells up untill then. To acheive this, they need 5.8 Ah cells. This was the first time I saw a battery with these cells, so I'd call them new battery tech.

You provide a bit of info here that I'm not sure is correct. The old 5 Ah cells are close to 70 g, claimed weight for the Samsung 50E 21700 5 Ah is 68.7g. The LG M58T is about 3g heavier than the Panasonic 5Ah cell, at 71.7g. INR21700-M58T

I don't think the cells are discharged as low as 2.5 V for this application. And most battery packs should have no problem delivering all the current a full-power motor can draw at well below 50% soc (36V). It requires about 20 A to deliver 700 W at 36 V. That's ~5 A drawn from each cell for a 10s4p pack, well below the rated max discharge of 10.8A for the M58T. You need low cell temperature and/or even lower charge before the cells are pushed to their limit. The new 600-630 Wh battery packs will be asked to deliver 6.5 Ah to get 700 W at 36 V, that should still be fine. The 10s2p configuration will struggle though, and it's used with the 600 W Bosch SX motor. Bosch says it's fine as this motor will only peak at 600 W, riders aren't able to draw 600 W constinous riding the SX motor. But using the CX motor with the 400 Wh battery and the motor might start derating at 80% SOC, as this motor can have a more prolonged 600W output.

Hey, no worries, different views are great, not everything looks the same from a different perspektive .

Everything you say also makes sense, to some point I agree. Btw, where did you get the Giant's 22700 cell capacity from, because I could not find any credible info on them. For my claim of 5,7Ah I just did a reverse math calculation(rounded down) from a 21700 5,56Ah cell and it's weight.

Don't understand what you mean how can 65g 21700 5Ah cell have a higer energy density than a 22700 cell 68g 5,56Ah cell(of course if our claims about the 22700 are correct).
5Ah/65g = 0,0769Ah/g
5,56Ah/68g = 0,0818Ah/g

Corrected 》 Two years ago when the 22700 cell was first used by Giant I could not find any info on them, assumed there still weren't any when I wrote the article, did a little check, found that there are some. The only online mentioned made by Panasonic is the INR2270A 5800mah , 5,65Ah 21,8mm x 70,9mm 74,5g cell.

For cell energy density you probably meant the newer LG 5,56Ah cells right, because you wrote 5Ah?

Mid capacity 21700(Spesh 700Wh pack)
5Ah/65g = 0,0735Ah/g

High capacity 21700(new 800Wh packs)
5,5Ah/70g = 0,0786Ah/g

22700(Giant 800 and 400 Wh packs)
5,65Ah/74,5g = 0,0758Ah/g

The cell density difference in this cases is evident but really minimal. What is also evident is that with a 5Ah cell there are no 800Wh packs, you would need another P group, but that isn't possible to stack into existing packs.

Only the 2 year old 22700 cell and the "ebike world new" "eskate old tech" high capacity 21700 cells enable a 800Wh pack.

About the weights of cells I provided, I took those from technical specifications of cells in online shops with the capacity cca 5,5Ah...I didn't take a specific cell as it's impossible to find out which type, brand cell different manufacturers use, mostly all 21700 cells no matter the capacity range from 67g to 73g, with some exceptions, so I took a mid value.

For the Spesh 18650 cells with 5,8Ah capacity that's almost not possible, 18650 cells max out at cca 3,7Ah. I didn't look into detail about that, but It's a weird number, and I have not seen one in real life.

A cell with a high capacity has a higer internal resistance, hence it's ability to provide stable current throughout the whole SOC is greatly reduced compared to a 21700 with a capacity of 4,2Ah that has low internal resistance. A cell with lower internal resistance is able to put out double the amperage of a high capacity one. For smaller packs I would rather have the low capacity high current cells as that way the battery sag is almost not present.

I agree the current draw isn't huge with ebike motors that is why mid/high density cells(5Ah or more) are common. I also agree that with smaller packs the derating comes earlier in to the ride.

Why am I saying that there is no new battery tech, because my other hobby is eskate. I have seen high capacity 5Ah+ 21700 cells way before they were introduced in the ebike world. I run a 48V system 900Ah system on my eskate, compared to a 36V it's night ws day. I have high capacity 21700 5,1Ah cells, compared to low capacity 4,2Ah battery sag is present way before and the power feel is also completely different on the low capacity/high amperage cell systems.
Yes 2,5V is the low discharge cut off limit, I didn't wnat to go to much into technical detail, so the majority could understand better, don't know how low cells in ebike packs discharge, maybe someone in the industry can elaborate, but from experience in eskate the cells do get close to 2,9V when almost fully discharged.
One interesting tool we get in the eskate world is a Bluetooth BMS. With this you can monitor every cell in your pack via an app on the phone, you can see if a problem with a cell starts immediately and can so do preventive action before it's to late for the pack. I am not sure if any ebike manufacturer provides this? If it would it definitely would be new in the ebike world, but definitely not new tech in general.

So also in general I would not call the just slightly higer capacity cells in the 21700 format new tech but maybe just an evolution of the existing tech, that's why my problem with people claiming extreme battery pack densitys due to new battery tech.

I still claim that the most difference in pack(not cell) energy density(Wh/kg) comes from the housing material, it's implementation and the safety standards used.

 

[emtbeast]

What about a 48v motor system like the specialzed SL and fazua ride 60 motor.?

Hey,


A 48V system is just a system that works on 48V, a 48V rated motor, electronics(BMS) and a battery pack in a 13S4P, 13S3P, etc... configuration

13 x 3,65V cell ~ 48V

The advantage of it is even lower current, lower heat thus better efficiency. The catch is, creating a slim enough pack for a good looking bike, but it is possible with some thinking and good r&d.

I think a great example of good 36V battery pack r&d is the Spesh 700Wh pack in a slimm design.

I also have a feeling they are cooking something in the 48V realm for the next bike release.

 

[emtbeast]

Thank you for these interesting notes! May I ask about your background? Do you work in the industry?

Hey, my background is just a high-school degree in electronics,a hobby in eskate and a slight passion for electronics, I don't work in the industry, so I don't have a full outlook on everything, but try to follow the flow.

 

[Doomanic]

The term "Tech" needs clarifying IMO. To me, new battery "Tech" is stuff like solid state or different chemical composition' It's not more energy from the same cell type, that's down to marginal improvement in manufacturing techniques.

 

[emtbeast]

The term "Tech" needs clarifying IMO. To me, new battery "Tech" is stuff like solid state or different chemical composition' It's not more energy from the same cell type, that's down to marginal improvement in manufacturing techniques.

This I agree with

 

[irie]

The term "Tech" needs clarifying IMO. To me, new battery "Tech" is stuff like solid state or different chemical composition' It's not more energy from the same cell type, that's down to marginal improvement in manufacturing techniques.

Agree, these so-called tech advances are basically marginal improvements in cell performance and packaging.

 

[knut7]

Hey, no worries, different views are great, not everything looks the same from a different perspektive .

Everything you say also makes sense, to some point I agree. Btw, where did you get the Giant's 22700 cell capacity from, because I could not find any credible info on them. For my claim of 5,7Ah I just did a reverse math calculation(rounded down) from a 21700 5,56Ah cell and it's weight.

When doing the article about the Giant 400 Wh battery, I just calculated backwards using 20 cells and 3,6 V to arrive at 5.56 Ah, and it was a number I saw mentioned elsewhere at the time. But now that I've seen the specs sheet... I'm still confused. It states weight and size without the "tube"??? I'll just use the claimed numbers, but I'm not sure it's actually any more energy dense than the Panasonic 50E. Lithium ion Batteries - Panasonic Energy Co., Ltd.

Here's an overview including the old 18650 cells, the old 21700 5Ah cells, the new 21700 5.8 Ah cells and the Panasonic 22700. I've calculated the gravimetric and volumetric energy density based on the size and weight claimed in the spec sheets. It appears to be a tad higher than the corresponding figures claimed by the manufacturers, but it's fine for comparing these cells.

I usually go by gravimetric energy density when comparing cells. It says the same as the Ah/g numbers you calculated, but it's easier for me to relate to Wh/kg.

Yeah, the cells are getting heavier. So we're not seing the 540 Wh battery pack (used by YT/Orbea/etc) becoming lighter due to improved cell chemistry. But that battery has now become a 630 Wh battery with a minimal increase in cell weight. Having a 630 Wh battery is nothing new, Shimano had one for years. And Bosch too, even though they labeled it 625. But those used 18650 cells.

A 630 Wh battery using 18650 cells is a 10s5p config, so it has 50 cells weighing 50g each for a total of 2.5 kg. The Orbea (etc) 630 Wh battery with 21700 cells is a 10s3p config. With 30 cells weighing 71.7g, we get 2,15 kg. Due to restrictions in cell designs, the improvements might not be apparent, but this example illustrates it nicely.

Just for "fun", lets have a look at the Bosch 750 Wh battery. It's got 60 18650 cells with a combined cell weight of 3 kg. An 835 Wh battery pack using 40 of the new 5.8 Ah 21700 cells has a combined cell weight of 2,87 kg. Not that much lighter, but with over 10% higher capacity.

I don't know who's to blame for calling this "new battery tech", hopefully not me, even though I've used that description But we are finally getting improved cell chemistry. The 3.5 Ah 18650 cell reached ebikes in around 2016. Then we had a very slight, dear I say theoretical, increase when the 5 Ah 21700 cells appeared for 2019/2020. It was still the same chemistry and we had to wait about 8 years after 2016 to get a noticeable improvment in battery tech, I mean cell chemistry The 2016 cells were called high-nickel cells. The new ones are ultra high nickel. So, one might argue it's still the same "tech".

 

[Waynemarlow]

Be careful guys with using " optimal max " figures such as you are quoting. So far you haven't mentioned that the manufacturers to build in longevity of the cell groups will only discharge to around 3.1V. Below that and the cell life span becomes somewhat deminished. Equally charging to the full 4.25V is rarely done, to gain those last few Wh's will decrease the cell life somewhat.

My guess without taking recordings of what Bosch and the likes are doing is that you will be only able to fully use probably around 90 - 95% Wh over quoted max battery manufacturer figures. To give some idea my 52V packs at 14S3P should be a 780W pack. The most I have ever been able to charge is 730Wh from a fully EBike discharged battery. The motor I use turns off the pack if any of the cells drop below 3.0V

Also at lower voltages it is rare to be able to pull any sort of amps ( the high amp cells designed to do this have less total storage ), hence its why the likes of Bosch turn the power rating down signficantly from about 80% discharged. The Samsung 21700 cell most are using will not be able to supply much more than 1 -2 amps below about 3.1V. From actual experience and recording, anymore than that and the voltage will sag sufficient to trigger the BMS shutoff, even though you still have some 50 - 100Wh left in the pack. We ourselves found the 40T ( 4A ) versions giving longer ride times than the 50T versions if we used them in 2P rather than the 3P packs just for this very reason. There are now some cells which can output higher amps at lower voltages, but come at a significant cost increase.

You also have the problem that the newer types of cells which the auto makers are using ( they are the force behind all the developments through shear numbers required ) although have an equivalent approx. total power output, have a significant increase in size to achieve that. At the moment Auto and solar storage are the big drivers of design. Our Ebike requirements are at best niche and unlikely to have much R&D thrown at it in the short term.

Sorry to say it but I would say in the short to near future, the 5.6A cells are here to stay.

 

[knut7]

I'm using the nominal figures. Sure they're unrealistic and we aren'table to access the full nominal capacity of a battery cell. But it doesn't really matter as long as we're just comparing cells, it tells us the difference between cells. We are getting a certain range from a 500Wh battery, and it seems comparable between brands.

I have considered looking into the net capacity of these batteries... The voltage drops quickly at both extremes, so we're not missing as much energy as one might expect. Although I assume there is a noticeable chunk of energy left at the low end.

 

[emtbeast]

Be careful guys with using " optimal max " figures such as you are quoting. So far you haven't mentioned that the manufacturers to build in longevity of the cell groups will only discharge to around 3.1V. Below that and the cell life span becomes somewhat deminished. Equally charging to the full 4.25V is rarely done, to gain those last few Wh's will decrease the cell life somewhat.

My guess without taking recordings of what Bosch and the likes are doing is that you will be only able to fully use probably around 90 - 95% Wh over quoted max battery manufacturer figures. To give some idea my 52V packs at 14S3P should be a 780W pack. The most I have ever been able to charge is 730Wh from a fully EBike discharged battery. The motor I use turns off the pack if any of the cells drop below 3.0V

Also at lower voltages it is rare to be able to pull any sort of amps ( the high amp cells designed to do this have less total storage ), hence its why the likes of Bosch turn the power rating down signficantly from about 80% discharged. The Samsung 21700 cell most are using will not be able to supply much more than 1 -2 amps below about 3.1V. From actual experience and recording, anymore than that and the voltage will sag sufficient to trigger the BMS shutoff, even though you still have some 50 - 100Wh left in the pack. We ourselves found the 40T ( 4A ) versions giving longer ride times than the 50T versions if we used them in 2P rather than the 3P packs just for this very reason. There are now some cells which can output higher amps at lower voltages, but come at a significant cost increase.

You also have the problem that the newer types of cells which the auto makers are using ( they are the force behind all the developments through shear numbers required ) although have an equivalent approx. total power output, have a significant increase in size to achieve that. At the moment Auto and solar storage are the big drivers of design. Our Ebike requirements are at best niche and unlikely to have much R&D thrown at it in the short term.

Sorry to say it but I would say in the short to near future, the 5.6A cells are here to stay.

Thanks for your input, I am/was totally aware of the cell charge/discharge voltage limits you mention. I just didn't want to go into to much detail to have a broder audience understand easier. The only way to find out what the pack really holds is to measure a charge from 0 to 100%.

Yes, the high capacity 5,5Ah+ 21700 cells have a few drawbacks like you mentioned the aperage delivery stability and longevity is not really good with these cells because of higher internal resistance.
I would also be happier with cells like the Molicel P42A 4,2Ah or the newer P45B 4,5Ah, because of their low internal resistance they can deliver a stable an also much higher currents throughout their SOC. But like you wrote, the cost difference is quite huge between the later mentioned and the high capacity 21700 cells.

 

[emtbeast]

When doing the article about the Giant 400 Wh battery, I just calculated backwards using 20 cells and 3,6 V to arrive at 5.56 Ah, and it was a number I saw mentioned elsewhere at the time. But now that I've seen the specs sheet... I'm still confused. It states weight and size without the "tube"??? I'll just use the claimed numbers, but I'm not sure it's actually any more energy dense than the Panasonic 50E. Lithium ion Batteries - Panasonic Energy Co., Ltd.

Here's an overview including the old 18650 cells, the old 21700 5Ah cells, the new 21700 5.8 Ah cells and the Panasonic 22700. I've calculated the gravimetric and volumetric energy density based on the size and weight claimed in the spec sheets. It appears to be a tad higher than the corresponding figures claimed by the manufacturers, but it's fine for comparing these cells.

View attachment 151433

I usually go by gravimetric energy density when comparing cells. It says the same as the Ah/g numbers you calculated, but it's easier for me to relate to Wh/kg.

Yeah, the cells are getting heavier. So we're not seing the 540 Wh battery pack (used by YT/Orbea/etc) becoming lighter due to improved cell chemistry. But that battery has now become a 630 Wh battery with a minimal increase in cell weight. Having a 630 Wh battery is nothing new, Shimano had one for years. And Bosch too, even though they labeled it 625. But those used 18650 cells.

A 630 Wh battery using 18650 cells is a 10s5p config, so it has 50 cells weighing 50g each for a total of 2.5 kg. The Orbea (etc) 630 Wh battery with 21700 cells is a 10s3p config. With 30 cells weighing 71.7g, we get 2,15 kg. Due to restrictions in cell designs, the improvements might not be apparent, but this example illustrates it nicely.

Just for "fun", lets have a look at the Bosch 750 Wh battery. It's got 60 18650 cells with a combined cell weight of 3 kg. An 835 Wh battery pack using 40 of the new 5.8 Ah 21700 cells has a combined cell weight of 2,87 kg. Not that much lighter, but with over 10% higher capacity.

I don't know who's to blame for calling this "new battery tech", hopefully not me, even though I've used that description But we are finally getting improved cell chemistry. The 3.5 Ah 18650 cell reached ebikes in around 2016. Then we had a very slight, dear I say theoretical, increase when the 5 Ah 21700 cells appeared for 2019/2020. It was still the same chemistry and we had to wait about 8 years after 2016 to get a noticeable improvment in battery tech, I mean cell chemistry The 2016 cells were called high-nickel cells (NMC911). The new ones are ultra high nickel. So, one might argue it's still the same "tech".

The tube that is mentioned is just the cell wrapping.
There are a few big manufacturers of cells on the world, Panasonic, LG, Molicel,...
The cell that comes from a factory has no wrapping, the outer is just metal
Then there are resellers(NKON, EVVA,Littokala,Batemo,...)that use their own wrapping with one of the big manufacturers cells inside.

The LG M58T you mentioned for the comparison has dimensions of:

LG INR21700-M58T (5570 mAh)

So first results added to the comparison here: Cycle life tests of High Energy density cylindrical cells | Endless Sphere Unfortunately, due to the declared larger dimensions D: 21.7 mm and H: 71 mm, the volumetric energy density is only 768 Wh/l and therefore the “magic” value of 800 Wh/l in...

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21,4mm x 70,5mm 70,8g without tube
21,6mm x 71,8mm 71,8g with tube

The manufacturers are slightly increasing the housing of the cells to increase their capacity to a point where they still fit in todays appliances. An example is the mentioned LG that is straight in the middle in thickness between the 21700 and 22700 and actually longer(71mm)than standard 21700 is. While the Panasonic NCR2270A Giant use is nearer to 22mm x 71mm by dimensions(21,89mm x 70,9mm), thus the designation 22700.

Panasonic NCR2270A 21700 22700 5800mAh 2C battery cell 3.6V - QueenBattery

NCR2270A 22700 5800mAh 2C

queenbattery.com.cn

Introduction of Panasonic NCR2270A,highest capacity of 21700 Battery NEWS EVVA-High End Lithium ion Battery Expert

EVVA is a professional developer and manufacturer dedicated to providing high end lithium ion power solutions for different applications. With experienced battery experience and advanced technology, it has achieved international high reputation for lithium ion cells supply and battery packs...

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Like you already pointed out in the previous post, the less the cells a pack has, the higher the current the cells need to deliver. So smaller packs will suffer battery sag sooner. Especially packs with high capacity cells as those have high internal resistance and can only deliver stable current for a limited time before they overheat and bms jumps in to derate them.

Currently the highest energy density pack is the Djis 800Wh it's mostly a result of slightly bigger high capacity LGs 21700 cells, probably original from the factory, light holders, and an extremely thin cca 2mm or probably even less housing. While this is great I personally am not a fan of high capacity cells. In eskate the battery pack drives 2 motors, and the low capacity/high amperage cells(Molicel P42A) work so much better, basically no battery sag almost to 10%, the high capacity 5,5Ah cells start saging at 25%.

Like I and other said untill solid state battery technology enters the ebike stage all new things mentioned by marketing untill now are just marginal gains in cell packaging, chemistry and pack packaging, no new technology.

With the term "new battery tech" I was referring to a wider group of people doing such claims, was not pointed specifically

 

[emtbeast]

Not all battery housings are aluminium though. Canyon's infamous cracking pack looks to be plastic.

Yep true, I was really surprised when I first saw their new packs, first thought was overheating. There is currently also a callback for their packs being faulty, not sure why exactly. I didn't know they also crack.

 

[knut7]

(...)
Like I and other said untill solid state battery technology enters the ebike stage all new things mentioned by marketing untill now are just marginal gains in cell packaging, chemistry and pack packaging, no new technology.

With the term "new battery tech" I was referring to a wider group of people doing such claims, was not pointed specifically

Yeah, it's down to expectations I guess. The ~10% increase from 260 Wh/kg might not sound like much. But I've waited for years to have improved cell chemistry in ebikes, so I'm happy to see any progress. And if the FEB 6 Ah cell is legit, the 10s3p pack becomes 650 Wh, that sounds nice to me.

But I too am of course waiting for the li-metal anodes to become less suicidal so we get high density solid state batteries! 800 Wh/kg is mentioned "frequently". That would turn my favourite 10s3p 21700 pack into a 1.490 Wh battery. But I (we?) don't know what form factor such cells would be available in. And I don't know the max continous discharge current. So I don't know if this cell configuration is an option. I assume the voltage would be comparable since it's Li based.

Yeah, power-density is a factor too. The most energy dense cells won't output a high continous current/power. The LG M58T is rated at 10.8A continous though, a tad more than the Samsung 50E at 9.8A. Both energy density and power density has increased, not too bad I think.

 

[The EMF]

Hello ebike community.

I am seeing a lot of talk out there about new battery tech, high energy density etc...and it's giving me a bit of a headache seeing how easy it is for brands to wash people's minds with some easy marketing bs.

WOW……
I'm opening this thread for talk about new ebike energy pack tech improvements on energy density and similar.

I will take the newer 800Wh packs, as those are the ones recently a lot of talk is about high energy density without any real or lack of explanation why so.

It will be a bit lengthy post so Let's dig in...

Shortly said, currently there is no new market available new magic battery tech going on at any brands packs period! For example the so called "new tech" has been already out there for at least 2 years(Giant 800Wh pack).

All 36V 800Wh battery packs out there use the industry standard high capacity 21700(21mm x 70mm) 3,6V 5,5Ah cells.

Maybe someone will correct me, so a note here: the cells in the Giant 800Wh packs are actually not industry standard as they are made exclusively for Giant by Panasonic and are a 22700(22mm x 71mm) cells, so slightly thicker and so have a slightly higher capacity of 5,65Ah and so slightly superior in some factors to other industry standard 21700 cells as larger cells bring increased energy density per cell, the battery heats up less, due to a slightly higher capacity it can operate in the optimal SOC window for longer and its lifetime is so extended. At this point we could go into cell chemistry etc, but for the low current draw of electric motors on ebikes that's basically an irrelevant factor.

All 36V system 800Wh ebike battery packs use 40 cells in a 10S4P electrical configuration(10 cells connected in series = 10 x 3,6V = 36V) and 4 series groups connected in parallel. It physically can't be done any other way because you need 10 cells connected in series to get 36V needed for the system. When you reduce the parallel connected series groups the lower the capacity of the pack and also smaller and lighter the pack, i. e. 600Wh with a 10S3P configuration with 30 cells.

Informational notes:
1. The cells when fully charged have a voltage of cca 4,2V(the whole pack 42V), when discharged fully the cell voltage drops to a minimum limit of cca 2,5V(the whole pack 25V).

2. As the motor is rated at 36V by specs, once the battery pack voltage when discharging starts falling under 36V, a rider starts to feel decreased system power, faster discharging of the pack or in other words the so called battery sag.

Going further, the only difference between different 800Wh packs is how the 40 cells are stacked inside the housing, the used BMS and cell holder material, hence the housing dimensions.

The Dji 800Wh(dimensions of 561mm x 71mm x 49mm) looking from one side the cells are most likely stacked in a 7(length) x 3(width) x2(height) configuration. That configuration leaves cca 6cm x 5cm room for the BMS, the connector and wiring. The configuration internally takes about 70mm in width and 45mm in height(including cell holders), looking at the dimensions of the pack that means the housing walls are cca 2mm - 2,2mm thick.

The new Bosch 800Wh(dimensions of 424mm x 77mm x 71mm) most probably has the cells stacked in 5(length) x 3(width) x3(height) configuration. This configuration ensures a lower and closer to the middle of the bike center of gravity especially if the empty space for the BMS is placed at the top of the pack.

So we have tradeoff here:
Dji - lower weight/higher out placed center of gravity
Bosch - higher weight/lower and more mid placed center of gravity

Battery cell weights:
A typical 21700 cell weighs cca 65g.
As there are no weight specs for the 22700 cells, doing some simple reverse math magic brings us to 68g. Corrected, two years ago when I was looking for info on the 22700 cells there were none as the they were brand new. I did a check up and found some info on them so the weight is cca 75g per cell, the capacity is cca 5,65Ah as predicted by my calculations. I corrected all the other Giant calculations accordingly.

40 x 21700 cell x 65g = 2,6kg
40 x 22700 cell x 75g = 3,0kg

Weight comparison of three 800Wh packs 》

The Dji 800wh pack is cca 3,74kg.
So the housing with the rest of the internals(BMS, wiring, connector, cell holders,...) is cca 1,14kg.

The new Bosch 800Wh is cca 3,9kg.
So the housing with the rest of the internals(BMS, wiring, connector, cell holders,...) is cca 1,3kg.

The Giant 800Wh is cca 4,3kg.
So the housing with the rest of the internals(BMS,wiring, connector, cell holders,...) is cca 1,3kg.

The most weight savings at current ebike batterys come from the housing material choice, it's thickness, implementation and safety standards manufacturers choose to use, the highest being the EN50604 (safety standard for lithium batteries for LEV - Light Electric Vehicles). Some manufacturers(i. e. Giant) go for highest safety standards(increase weight), other's use lower standards(lower weight).
All used standards must still ensure appropriate levels of safety prescribe by each countrys regulatory institutions.

Some thoughts on: how to get the battery weight down more - enter specific material density:

For this I'm not 100% sure(there is no spec data on battery housing materials) but I'm pretty sure most manufacturers use aluminum or PETE/PVC.

Different material densitys:
2,7g/cm³ ALUMINUM
2,2g/cm³ CARBON = (Alu - 18%)
1,7g/cm³ MAGNESIUM = (Alu - 37%)
1,2g/cm³ PETE/PVC = (Alu - 55%)

An Example:
The Giant 800Wh pack weighs cca 4,3kg. As already pointed out up the housing is made out of aluminum and weighs 1,3kg(with internals).
For this example let's say 0,3kg are the internals. So we have 1,0kg of pure aluminum housing. If this housing was made of magnesium we can deduct 37% of weight as the specific density of magnesium is 37% lower than aluminum.

1,0kg - 37% = 0,63kg

At a 0,4kg difference it would mean a Giant 800Wh pack with a magnesium housing would weigh 3,9kg.

Other examples:
A Dji 800Wh pack with a magnesium housing would weigh cca 0,4kg less about 3,3 kg

A Bosch 800Wh pack with a magnesium housing would weigh cca 0,5kg less about 3,4kg

Of course there is the cost aspect, but IMO as the amount of material used for each battery is minimal it shouldn't affect the price per pack for the end consumer to much as:

1kg of aluminum is 2,6€.
1kg of magnesium is 5,9€.

Aluminum housing:
1,4kg x 2,6€/kg = 3,64€

Magnesium housing:
0,88kg x 5,9€/kg = 5,20€

But of course as usual in todays world the manufacturers would market the bs out of a new lightweight magnesium battery housing and skyrocket the prices for the end consumers...

Another way to further decrease weight would be using thiner thus lighter housing walls shaped in a way that increases structural rigidity(i. e. wave, zigzag, pattern - already used by some manufacturers in a mild form).

Most probably it's the cost of manufacturing and the cost/availability of material why magnesium isn't used for the mentioned application. Maybe someone from the actual industry can elaborate further.

Efficiency and energy density of batterys due to the housing materials:
Some manufacturers use plastic materials for their batterys to reduce weight, while this is great for high weight savings it's not so great from safety concerns and heat dissipation reasons. A metal housing dissipates heat much better and so aids to increased efficiency.

To conclude, a higer ebike battery energy density does not come from some special new magical cells new or battery technology like a lot of talk about it is out there, but from plain simple housing material choice, it's implementation and the chosen safety standards.

IMO the breakthrough however will come when a first manufacturer uses an industry standard solid state battery specialy made for ebikes, that will drastically lower the weight at the same or even higher capacity rates. Current best ebike battery energy densitys hover around 200Wh/kg. A solid state battery could raise that to a realistic 300Wh/kg.
That would mean we could have a 600Wh pack at 2kg or 900Wh pack at 3kg. I know the form factor is a question here and we are still probably far away from a market ready product, but I am sure if an average Joe(here) is thinking about it, somewhere out there is a company thinking the same or maybe it's already in the r&d stage.

Going of topic a bit for the end, a high battery energy density isn't everything, especially not on an emtb, as previously mentioned IMO by lowering the center of gravity, more emphasis is placed on making the ride more enjoyable and efficient especially on emtbs ...while ensuring the same specs as the competition, that's what really counts at an emtb development. I have a feeling that only a few brands go so deep at development, but usually those bring out a ride that is amazing on the trails.

Hope all this makes some sense and helps clear up things about energy density and maybe get a good discussion down the road.

 

[Waynemarlow]

Yeah, power-density is a factor too. The most energy dense cells won't output a high continous current/power. The LG M58T is rated at 10.8A continous though, a tad more than the Samsung 50E at 9.8A. Both energy density and power density has increased, not too bad I think.

@knut7, if you want to go down the Samsung route then have a look at the 50S version, 5.0A and 35A max draw and only a euro or so more. Great battery if you could buy them, always out of stock everytime I've looked, I wonder why.

The big question is if we know that the batteries voltage at the bottom end in particular falls really fast under even small loads, then why do the manufacturers persist in using 36V. If they were to use say 52 volts then even at 1.0A draw on each cell, you still have approx 200W's. ( at 36V would be approx 140 or so ) Most of the tinkerers and experimentors of Ebike motors have long since abandoned 36 volts, moved to 48V's 10 years ago, moved to 52V's 5 years ago and now at 72V's. They have a lot of reasons for doing so. Surely if you want increased battery performance then the greater gains could be made in voltage selection together with very high density low max current cell selection.

 

[emtbeast]

@knut7, if you want to go down the Samsung route then have a look at the 50S version, 5.0A and 35A max draw and only a euro or so more. Great battery if you could buy them, always out of stock everytime I've looked, I wonder why.

The big question is if we know that the batteries voltage at the bottom end in particular falls really fast under even small loads, then why do the manufacturers persist in using 36V. If they were to use say 52 volts then even at 1.0A draw on each cell, you still have approx 200W's. ( at 36V would be approx 140 or so ) Most of the tinkerers and experimentors of Ebike motors have long since abandoned 36 volts, moved to 48V's 10 years ago, moved to 52V's 5 years ago and now at 72V's. They have a lot of reasons for doing so. Surely if you want increased battery performance then the greater gains could be made in voltage selection together with very high density low max current cell selection.

Good thinking right there in the last part , that's a good point where an advantage of a higher voltage systems is.

Not sure either why, but Imo it's is the cost aspect on why most are still sticking with 36V.

The 50S is a good capacity cell with really decent specs overall. If I'm not mistaken ONSRA Eskate company use them in their newest boards.

 

[timo2824]

@knut7, if you want to go down the Samsung route then have a look at the 50S version, 5.0A and 35A max draw and only a euro or so more. Great battery if you could buy them, always out of stock everytime I've looked, I wonder why.

The big question is if we know that the batteries voltage at the bottom end in particular falls really fast under even small loads, then why do the manufacturers persist in using 36V. If they were to use say 52 volts then even at 1.0A draw on each cell, you still have approx 200W's. ( at 36V would be approx 140 or so ) Most of the tinkerers and experimentors of Ebike motors have long since abandoned 36 volts, moved to 48V's 10 years ago, moved to 52V's 5 years ago and now at 72V's. They have a lot of reasons for doing so. Surely if you want increased battery performance then the greater gains could be made in voltage selection together with very high density low max current cell selection.

Once you exceed 40 volts then OSHA regulations kick in. For work anything over 40 volts and I'm supposed to wear rubber gloves, arch flash rated shirt/pants, ear plugs, safety glasses, and helmet with arch shield.

 

[Waynemarlow]

Yes you are correct that regs will kick in above 40V's. I think from memory 24V's with wet fingers and body will do the job of disrupting the heart rythym that on some of poor health, can be a problem.

But then your average 240V AC socket will kill you as well. How do we put up with those pesky sockets all around us ?

 

[knut7]

@knut7, if you want to go down the Samsung route then have a look at the 50S version, 5.0A and 35A max draw and only a euro or so more. Great battery if you could buy them, always out of stock everytime I've looked, I wonder why.

NIce. I've only been focusing on energy density the last few years. Either it was a typo or it's a measurement after different standard, but it seems the Samsung 50S is 25A continous discharge according to the spec sheet I read. Regardless, that's impressive. It should be enough to run a full power motor with a 10sp1 configuration. And in a 10s2p config, there should be little energy lost to heat at low SOC.

------------------------------------------

Going 48V isn't automatically an advantage. Comparing a 39 cell (13s3p) 48 V pack to a 40 cell (10s4p) 36 V pack, the 48V pack will be asked to deliver a lower current, but the 36 V will be able to deliver a higher current using the same cells. Wasn't it Specialized that built a 13s1p 160 Wh range extender using 3400mAh 18650 cells? It seems a nice design to get the necessary current capacity while keeping it small and light.

I wasn't aware of the US 40 V rule, in EU it's 50V AC and 75V DC.

 

[Waynemarlow]

75V DC.

Man that would pack a punch. I've inadvertantly touched across my 52V battery with dry fingers, I won't do that again .

 

[Waynemarlow]

but the 36 V will be able to deliver a higher current using the same cells.

Technically one could argue that the 48V pack would require a lower amperage if we take Watts as the deciding end result factor

 

[knut7]

Technically one could argue that the 48V pack would require a lower amperage if we take Watts as the deciding end result factor

Yeah, that's what I meant by "the 48V pack will be asked to deliver a lower current"

Using a 10A cell, the 13s3p pack would deliver 30 A max while the 10s4p would do 40A. A 600W motor would draw 13A at 48V and 17A at 36V (excluding loss). Pretty much 43% of max continous discharge current for both configs.

 

[Waynemarlow]

And that is part of the reasoning of the higher volts, 13A's is not unreasonable in regards to wiring size, cooling and torque produced by the motor stators. Get above 15A - 20A's and you have quite a leap in size of the mass of the interconnectors, wiring and stator sizes to cope with the added amps and heat.

Its all a trade off however and with the modern computer management of the engine, better design and closer engineering tolerances, manufacturers have a wide choice of parameters to deal with, all to get an output that you and I enjoy. Sadly the motor itself ( first designed way back in the 1820's ) has not until recently had the R&D it perhaps should have enjoyed.

 

[emtbeast]

And that is part of the reasoning of the higher volts, 13A's is not unreasonable in regards to wiring size, cooling and torque produced by the motor stators. Get above 15A - 20A's and you have quite a leap in size of the mass of the interconnectors, wiring and stator sizes to cope with the added amps and heat.

Its all a trade off however and with the modern computer management of the engine, better design and closer engineering tolerances, manufacturers have a wide choice of parameters to deal with, all to get an output that you and I enjoy. Sadly the motor itself ( first designed way back in the 1820's ) has not until recently had the R&D it perhaps should have enjoyed.

Agree, the motor on higher voltage can due to lower current have thiner coil wiring, less weight, less heat buildup in an enclosed space, better magnet efficiency, better overall efficiency. One interesting example could be the Pinion MGU, it's thermal stability was most probably the best in the Velomotion's test. While the Avinox is obviously implementing some different tactics to keep it cool and under the regulatory EU (250W average) radar. The Pinion MGU is an industry avaliable motor, so there is definitely room for improvement for ebike applications.

 

[knut7]

I don't think 36 vs 48 V makes much of a difference in this application. In most cases, the power wire is very short so increasing the gauge doesn't carry much of a weight penalty.

Interesting graph, did they make one that shows Nm rather than percent of max output too? And it would be interesting to see how things look between 15 and 30 mins. The Pinion seems to do well, but it makes sense that a bigger motor with more mass requires more time to reach the temperature threshold. It's not necessarily down to efficiency.

Edit: Found the article, the DJI did cut completely after about 20 mins, too bad they didn't extend the run for some of the other motors too.