Overcharging?

[GizmoSL]

I just bought an electric vehicle, a car that is, and one of the things I learned from the dealer was to never charge your battery to 100%, unless you were going on a long trip. The battery would last longer and give you better overall performance in the long run if you charged it to 80% capacity. You can actually set your vehicle to stop charging when it reaches 80%. This is a general rule of thumb for all Lithium based batteries, evidently. Well, it started me thinking about ebike charging. I think most of us have charged our bike's batteries to the limit every time, to get the maximum range from the battery, but like driving the electric automobile around town, most rides aren't long enough to fully drain the battery.
I started a ride with 80% charge yesterday, rode 24 typical miles on mixed terrain (climbs descents, singletrack, etc.) and had 40% battery life remaining. I kept the motor in turbo mode the entire time to make it a little more demanding. Makers of lithium based batteries recommend applying the 40-80 rule for their products, that is, keep the charge between 40 and 80 percent. Everytime we charge a lithium based battery, the performance is degraded, by the heat that the charge creates, and the charging that takes place between 80 and 100% takes longer percentage-wise. Anyway, just throwing all this out there as food for thought. We do spend a lot of time thinking and talking about our batteries. And all this info is accurate as far as I can tell, but if anyone can offer contradictory info, please weigh in.

 

[Beekeeper]

Agreed, lithium ions should not be charged to 100% and I’m pretty sure when chargers cut out, your cells will be significantly less than 100% in order to protect them.

batteries will degrade over time whether you use them or not. The slow death starts the moment they leave the factory. If I only charged to 80% I’d feel I was purposely handicapping myself.

After a ride I top up to 50% and store it at that.
just before a ride I charge until the charger cuts out.

 

[DtEW]

You're definitely on the right track, OP. All this is obvious to people who own electric cars. It is obvious to (an admittedly smaller crowd of people) who have deeper experience with rechargeable batteries, eg. people who have been involved in R/C racing. But on-the-whole, you are correct that this is a foreign paradigm to the e-bike community. Sometimes you'll even get pushback. Sometimes the funny assertion that e-bike power systems are built with greater margins than the obviously less-mass-sensitive electric car power systems, and that what's accepted to be bad for the electric car is somehow not going to be bad for the e-bike.

Well, the upside is that e-bike batteries are indeed cheaper and easier to replace when they fail compared to electric car batteries.

 

[Beekeeper]

All this is obvious to people who own electric cars. It is obvious to (an admittedly smaller crowd of people) who have deeper experience with rechargeable batteries, eg. people who have been involved in R/C racing. But on-the-whole, you are correct that this is a foreign paradigm to the e-bike community. Sometimes you'll even get pushback. Sometimes the funny assertion that e-bike batteries are built with greater margins on both ends than the less-mass-sensitive electric car battery, and that what's accepted to be bad for the electric car is somehow not going to be bad for the e-bike.

Well, the upside is that the e-bike battery is cheaper and easier to replace when they fail compared to an electric car battery.

Agree with the cost. Just bought a brand new spare 500wh Bosch for £550. We are now doing longer rides. Considering the use I’ll get out of this and the number of years use, I don’t regret the payment one bit.
Eliminating range anxiety....... priceless ?

 

[Smittylube]

I’ve been flying electric RC helicopters for more than a decade .
lipo packs originally had low ‘C’ ratings meaning charge and discharge rates Based on capacity.
Over time these numbers improved. Basically more power out faster and ok to charge faster than previous versions..
lipo means lithium polymer
lion means lithium Ion.
both have different chemistry and volatility.
Lipo is know to be less stable and deliver power faster.
From what I understand the heat you don’t want is discharging as charging can actually cool the pack.

I use a charger that gives me options to fast or slow charge while balancing the individual cells. Additionally I can see the I R of the cells as well.
when the internal resistance goes up the voltage delivery goes down.
Unfortunately we have no way of seeing the MA volume with the chargers supplied.

Additionally or FYI what we do to get the power is raise the voltage by #cells times S meaning each cell is roughly 4v charged so say 5 cells in series means 20v 10 cells 40v for me flying my small heli used 6s or 24v and my ‘700’s use 12s or 48v
when you raise the voltage the current goes down and power goes up. This is how the hybrid cars work. Something like 250-325v.

I believe I was told by my lbs our rail battery is lithium Ion. These are more stable overall, and I believe less of a problem going over 80%. Less or no ‘memory’. Meaning if you run full to 1/2 and recharge it won’t lower the capacity. (Mah)

I charge my lipos 1/2 way for storage. And 95/100 to fly. Try and leave at least 20% because that’s where they puff and get hot.

The way I understand it is if you full charge and ride right away or within say a Day you are not degrading the pack. Additionally I would not suggest leaving the pack empty. I would still try for 1/2 charge if its going to sit.

 

[GizmoSL]

Rekt may have put it all to rest. Overthinking is harder on the brain than overcharging is on the battery. No more posts, we have a winner.
I was most likely high when that came to me.

 

[Mteam]

Yep life's too short to worry about ebike battery charge levels.

 

[Beekeeper]

That’s settled then. Get ready for the power cuts tonight as everyone plugs in their chargers at exactly the same time ?

 

[flash]

You're definitely on the right track, OP. All this is obvious to people who own electric cars. It is obvious to (an admittedly smaller crowd of people) who have deeper experience with rechargeable batteries, eg. people who have been involved in R/C racing. But on-the-whole, you are correct that this is a foreign paradigm to the e-bike community. Sometimes you'll even get pushback. Sometimes the funny assertion that e-bike power systems are built with greater margins than the obviously less-mass-sensitive electric car power systems, and that what's accepted to be bad for the electric car is somehow not going to be bad for the e-bike.

Well, the upside is that e-bike batteries are indeed cheaper and easier to replace when they fail compared to electric car batteries.

It'll depend on what BMS is in the system. RC LiPO's generally don't have an inbuilt BMS at all so you're on your own. Consumer devices mostly have limiting BMs's in them.

The assumption comes from the information supplied by the manufacturers. Most of our eBike batteries have ratings for at least 1000 cycles. Based on common data for LiOn batteries they are usually rated for 500 cycles at 100% and 1000 cycles at 80%. Therefore it's likely that the BMS has been set to an 80% of cycle charge. Can't say that it's true. Haven't bothered to test. But the assumption is reasonable. Different systems have different levels of strategy. My LiPO packs in my hexacopters have no BMS internally. The LiFePO4 batteries in my caravan have a BMS that limits charge and discharge to 80/25%.

Anyway, the big issue is storage. LiOn doesn't like to be left at a high SoC. Store at 50-70% and charge before the ride. A 10 dollar timer makes that super easy.

Gordon

 

[Smittylube]

Great idea for a timer.
I say full charge it if your going to ride soon. and don't bother to worry about it.
LBS says remove battery if gone for more than 2 weeks. otherwise ride charge ride repeat.

 

[apac]

If you don't charge the pack to a high enough charge state the bms may not balance out the pack as this is done at the end of the charge when the charging process changes from constant current charging to constant voltage charging. It's at this point that the charger turns into a kind of trickle charger and only inputs a very small amount of amps. The bms will be pre programmed to start balancing at the very end of the charge and not when the cells are at 4v each.
In fact balancing will probably begin when the first cell reaches 4.2v. So under charging your pack could potentially lead to an out of balance battery pack which will eventually lead to a broken battery.

 

[GizmoSL]

My post generated some very informative responses, for which I am grateful. The batteries in our ebikes are more than just bricks to a lot of you. I'm impressed by the level of knowledge. So the takeaway is, as Smittylube said, "Charge, ride , repeat."

 

[Mikerb]

My Levo battery is over 2 years old. Charging to 100% probably only once every 6 weeks to let the charger balance the cells, other than that charged to c 85%. I have rarely ridden the battery below 3 bars on the TCU and I know if the ride is going to be c 25 miles a full charge will leave me with 3 bars on the TCU.....just a bout to change to 2. According to MC my battery condition is 100% still.

 

[urastus]

So under charging your pack could potentially lead to an out of balance battery pack which will eventually lead to a broken battery.

I think it's all in the detail. I was always told to do a balance charge once a month or so if riding regularly.

I use a timer, which is simple and easy and I don't have to give it any thought once it's set. My charger is slow and kind of back to front. It takes, supposedly, 6.5 hrs to charge from 0 - 80%, then just 1hr for the last 20%. Up to 80% it works out roughly to 1% of charge takes 255 seconds on the charger. If I need to charge it to 30%, then it's just 30x255= 7650 secs. Divide that by 60 to get minutes = 127minute = 2hrs 7mins. I now have a charge with various %'s and their relevant times so I don't do any calculations.

None of that matters much, I'm only concerned with the 1% and 255 seconds. If I'm going beyond 80% it is a balance charge, and I'll leave it on for too long so that it is not cut short eg 30mins or 1hr over. The charger stops by itself before the timer turns power off.

The other good thing about the timer is that you can start charging whenever you like. EG, if I'm doing a balance charge I'll try to finish it not long before I intend to ride. This way the battery is not spending much time in a full charge state.

The other great thing for charging to 80%, is that life happens! My last charge was to 80%, I was going to ride the following day - that was 3 weeks ago. I tore lower back muscle, it was nearly good after a week, then I tore it again. It has come good, but this week has seen flooding and high wind; I'm not into lots of wear and maintenance so I've been walking the dog. All that time I can feel at ease that the battery has been at 80% or less.

I've been charging everything like that now. The phone is easy, I just use it's clock timer.

 

[Growmac]

I frequently use 100% of the battery on a ride. Not unusual to have to ride the last 5 miles home with it completely flat. I've bought a second battery now which I'll carry with me if I think it's likely to be needed.

Despite efforts to otherwise be very nice to the batteries, they're both degrading at a spectacular rate, so I suspect there's A) something to this 80% theory. Maybe?, and B) a specific problem with Shimano E8035 batteries, as my Bosch riding friends are seeing nothing like the rate of decay that I am.

P.S. How long am I going to be a "new member" for? I've been here for months and posted a fair bit.

 

[Calsun]

If a battery pack is charged to 80% SOC and discharged to 20% SOC then only 60% of its capacity is being used and so one would expect it to last longer than if 80% of its charge capacity was being used each time before recharging. But I see no reason to use 75% of the available battery capacity so that a $500 battery will last a few months longer (and battery prices are falling).

What is damaging to batteries are overcharging and this is a problem with the cheap brick transformers / chargers being sold. It is why the battery makers caution against leaving the batteries plugged into the charger for long periods of time. Also with lithium batteries the charge rate slows as it reaches 95% SOC and seldom is there a good reason to charge much longer to get the additional 5%.

I would expect (and Apple voids the warranty for its products) more problems from recharging at 80% SOC instead of taking the battery down to 20% when it is practical to do so. And with pedals for power, unlike a EV car, there is a fall back if the battery SOC is too low to operate the bike.

 

[Mikerb]

I frequently use 100% of the battery on a ride. Not unusual to have to ride the last 5 miles home with it completely flat. I've bought a second battery now which I'll carry with me if I think it's likely to be needed.

Despite efforts to otherwise be very nice to the batteries, they're both degrading at a spectacular rate, so I suspect there's A) something to this 80% theory. Maybe?, and B) a specific problem with Shimano E8035 batteries, as my Bosch riding friends are seeing nothing like the rate of decay that I am.

P.S. How long am I going to be a "new member" for? I've been here for months and posted a fair bit.

not until you look after your batteries better

 

[taxidriver50005]

500 charges at 40 miles range is 20,000 miles are we worrying over nothing, I still charge to 80% but doubt myself somtimes

 

[urastus]

500 charges at 40 miles range is 20,000 miles are we worrying over nothing, I still charge to 80% but doubt myself somtimes

That is one form of deterioration, the other is time. Storing at 100% is where most of the damage can be done, from what I understand.

 

[Planemo]

If you don't charge the pack to a high enough charge state the bms may not balance out the pack as this is done at the end of the charge when the charging process changes from constant current charging to constant voltage charging. It's at this point that the charger turns into a kind of trickle charger and only inputs a very small amount of amps. The bms will be pre programmed to start balancing at the very end of the charge and not when the cells are at 4v each.
In fact balancing will probably begin when the first cell reaches 4.2v. So under charging your pack could potentially lead to an out of balance battery pack which will eventually lead to a broken battery.

Absolutely this. Whether people think charging to 80% or whatever is OK is nothing to do with cell chemistry and everything to do with how the charger/BMS works.

The VAST majority of li-ion charge systems use the 'dumb' method as mentioned above. That is, the system won't balance anything at all until a cell hits around 4.15v. Charging to 80% (or even 90%) means balancing will never happen and trust me it is the quickest way to ruin cells (other than over-discharging).

Don't think for a minute that this takes a lot of time either, cells can go out of balance within a few charges, and the worst thing is that no amount of charging will bring them back from the dead because even though the bleeding resistors will reduce current to any cell over 4.17v to allow more flow to lower cells, current still supplies the high cells and so they do still charge. As soon as a cell hits around 4.25v the system will shut down totally and any cell less than the required amount gets no more. Thats it. End of. Your pack is now imbalanced and unless you remove each and every cell to charge it individually it will never recover. The first sign of this is when your charger shows a green light way before it used to or pack voltage is below stated. Worse still, the lower voltage cells get worked harder, the imbalance gets greater every charge/discharge and the situation soon spirals out of control.

There ARE systems that can start balancing from the moment the charger is plugged in ('smart' chargers). I suspect high end systems such as Tesla may do this or in fact any system where the manufacturer says that partial charging is no problem. Whether the systems in our ebikes are 'smart' I couldn't confirm, and although the Bosch setup does seem a lot better designed than that in say my electric unicycles, I still wouldn't trust not charging to 100%, every time. My unicycles got imbalanced within just 4 partial charges, and to enough of an extent where using the stock charger was futile. the packs had to be stripped. Thankfully the cells were not damaged as they never went below 3.1v, but it was an arse of a job.

In short, partial charge at your own risk, unless specifically told by the manufacturer it is OK.

 

[Planemo]

That is one form of deterioration, the other is time. Storing at 100% is where most of the damage can be done, from what I understand.

Storing at 100%, whilst very damaging, is actually less damaging than partial charging.

A battery kept at 100% may last a year (think laptop batteries). A battery subjected to repeated partial charging may be useless within a couple of months. I would never go more than 2 partial charges before a full charge.

 

[Old Mike]

Storing at 100%, whilst very damaging, is actually less damaging than partial charging.

A battery kept at 100% may last a year (think laptop batteries). A battery subjected to repeated partial charging may be useless within a couple of months. I would never go more than 2 partial charges before a full charge.

Does 80% count as a partial recharge?

 

[Beekeeper]

The ebike battery technology in 1895 was far superior ?

They never exploded and you could trickle charge them forever. No need to set silly timers to come on in the middle of the night.

 

[Planemo]

Does 80% count as a partial recharge?

Yes, given that most bms' dont engage the balancing resistors until 4v at the earliest. Which is around 90%. The last 10% is where nearly all of the balancing occurs.

 

[DtEW]

Storing at 100%, whilst very damaging, is actually less damaging than partial charging.

A battery kept at 100% may last a year (think laptop batteries). A battery subjected to repeated partial charging may be useless within a couple of months. I would never go more than 2 partial charges before a full charge.

Holy hyperbole, Batman!

I guess all my Levos are useless now.

 

[alan_sh]

I love the theory, but in practice:

I ride, get back, clean the bike (maybe), plug it in, go indoors. I trust the charging 'brick' to know what it's doing. Repeat the next day.

I have no idea when it will hit 80% and I'm not standing over it until 4 (out of 5) lights have gone blue and stopped flashing. If the battery dies in 2 years time (which I think is about 500 charges), I'll replace it with my spare one. Or buy a new bike.

 

[Planemo]

I love the theory, but in practice:

I ride, get back, clean the bike (maybe), plug it in, go indoors. I trust the charging 'brick' to know what it's doing. Repeat the next day.

I have no idea when it will hit 80% and I'm not standing over it until 4 (out of 5) lights have gone blue and stopped flashing. If the battery dies in 2 years time (which I think is about 500 charges), I'll replace it with my spare one. Or buy a new bike.

Yep, the best way to do it

You're not partially charging and you're not leaving it stored at 100% for ages because you're riding it the next day. It's all good for you, your battery should last you well, far more than 2 years I would wager

 

[Planemo]

Holy hyperbole, Batman!

I guess all my Levos are useless now.

Re-read my post. I did say that it's possible our ebike systems can start balancing as soon as they are plugged in, rather than at the final 10%. They may not. I don't know. But I'm not taking the risk with my bike, given I have no confirmation from Bosch that partial charging is OK.

Storing at 100% is bad for li-ions, whatever the charge system. The longer it's stored, the worse the problem. If you ride the bike every day, or even every few days, it's not really a problem. Personally I don't leave mine longer than 2 days, but do what you like.

In any event, partial charging or storing at 100% won't render packs 'useless'. It's an accumulative process and it's impossible to ascertain the extent of cell damage without properly testing. Given the price of replacement packs (which are very much a big budget item for me) I want to do the best I can to prolong the life of mine. YMMV.

 

[alan_sh]

Yep, the best way to do it

You're not partially charging and you're not leaving it stored at 100% for ages because you're riding it the next day. It's all good for you, your battery should last you well, far more than 2 years I would wager

I think the charger helps too. When it gets to 100%, it switches off (the light goes to green) and all the charging lights on the bike battery go out. So, it is not pushing power in all the time

 

[Planemo]

I think the charger helps too. When it gets to 100%, it switches off (the light goes to green) and all the charging lights on the bike battery go out. So, it is not pushing power in all the time

Yeah, mine does that too. Pretty standard for a decent system, which I would expect Bosch to be tbh. It's certainly more 'intelligent' than some other systems as theres communication wires also involved rather than a simple positive and negative.