Bafang BBS02 cuts off when battery power reaches about 70%

[Seraye]

Hello,
I am having an issue with My BBS02 cutting out when my 48v mini cube battery reaches around 70% (about 50/51v). I have two mini cubes and this happens to both batteries, and ALWAYS at that level. I am very conservative with my power usage - I like to pedal and do not have a throttle, have my controller limited to 18 amps and I am a “spinner.” The power has cut out at all times in a flat mellow stretch of the ride.
I checked all connections - there is no visible damage at any of the connections and there are no loose connections, I use the EggRider display, and I even changed out the Motor controller (with a lunacycles improved controller) just in case.
As far as my batteries are concerned- I am very diligent about charging them to 80 or 90% if not in use (tho they are used every week if not daily- even in the winter) I have rarely drained them below 50% and I have never completely drained them. I always slow charge them (1 or 2 amp charge) and I Purchased an advanced charger that shows voltage - in the hopes of balancing the batteries - tho this does not appear to work (the charger cuts around 53-54 volts then turns off and will not come on again). I also bring my batteries inside if it is going to dip to freezing or colder (rare here).
Last detail - I use Anderson pole connectors.
—- so, I have searched the web far And wide for an answer to this issue- I have found numerous postings by individuals with the exact same
Problem - A power cut at about 70% this problem seems to always involve a bafang motor (searched for tsdz2 and found no posts about this problem) and happens with different types of batteries - 52v as well as 48volt. I have seen advice on steps to problem solve this issue - but all these feeds end without any real solution.
Oh - and some other details - these batteries worked are almost new - I have done numerous rides with no problem. One battery is more lightly used - probably not even 100 miles on it- the other battery has only about 300 miles on it - if that means anything.

And lastly - I have my set my controller to cut off at 39V.

:
1. Has anyone here had a definite solution to this problem? A solution that is tried and true for hundreds of miles?

2. Can anyone tell me if my Mini cubes have a BMS? Excuse my ignorance, I am learning here, but this is an issue with both of these batteries. I am a bit dismayed because they have so few miles on them and I purchased them last year (I think last year) . I have tried to balance them with my new charger but that doesn’t happen - I have turned off the charger let it sit for an hour then turned it on to top it off - I have done this over the course of a day - the battery approaches 54.4ish… but problem still occurs.

3 is it possible that I have damaged the bms of my batteries with too much disconnecting/reconnecting with the Anderson pole Connectors ? I do sometimes hear the spark and have only disconnected my batteries mybe half a dozen times now - I have ordered xt90 spark resistant connectors to avoid this.

I am dismayed that this is happening so early on- with fairly new and not abused parts. If the solution is purchasing a new battery - so be it - i’d like to have reliable battery power for
More than just a around town trips.

this seems to be a bafang issue andthe posts I’ve found about it have exactly the same issue if the battery cutting at 70%ish. I would appreciate any recommendations or information or anecdotes you might have about this issue.

And Please share if this is your experience.

 

[Waynemarlow]

You may want to put a diagnostic logger in line ( they are not expensive

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and see if the voltage is falling off significantly enough to trip the BMS. Do power the logger with a small battery though as they have no backup memory battery.

I’m not sure of the makeup of the battery but unless the cells are selected wisely you can run into problems with voltage fall off of even batteries at 70%. Try setting the max amps to say 10 amps and see if that changes things as I suspect 18 amps is quite a big draw off if you are reaching that sort of level.

But without knowing exactly the problem by using a logger of some kind, you are just firing off theories.

 

[Seraye]

The battery I have is the 6Ah 48V 30amp Samsung mini-cube with 30q cells. Don’t know if this would be helpful but here is the graph from EggRider of my ride showing the power cut - the first image is zoomed in.

 

[Neeko DeVinchi]

Hi @Seraye, I understand that you are running a BBS02 (UART protocol). This is made obvious due to you using the Eggrider v2 display.

Whilst I appreciate that you've been descriptive in your post, could you kindly post a screenshot of your parameters of your levels of assist for consideration?

Running the maximum current at 18amps is quite safe for that motor (hell, I've riders amend the maximum current to which they eventually run into problems).

I'll look into the battery you are using but the good news is that you're technically not locked in to a specific battery style (unlike the new M625). So if it is revealed that it a BMS issue (not saying that it is), then it would be a simple enough upgrade.

In the meantime, I'll ping a colleague of mine to see what we can work out but definitely screenshot the parameters of all three pages of the BBS02 for consideration

 

[Seraye]

Hi Neeko,
Here’s those screen shots. And yes, I may have to resign myself to purchasing new batteries, but it is baffling that it is happening to both of my batteries. At the time of this shut down I had the controller limited to 15.

 

[Neeko DeVinchi]

Bare with me @Seraye. I'll get back to you shortly. Just need to cross-reference a couple of things

 

[Waynemarlow]

That battery is failing at approximately 5.7 amps. The other battery is doing the same. One could almost eliminate the batteries.

My guess is you may want to check your electrical connections between motor and battery, even though they may look good, if they are of poor contact they will heat up until failing from the poor contact. You unplug the battery and reset the system, the contact is now working again and voila you have a working motor until you pull 300w’s again.

 

[Waynemarlow]

Actually there is a situation where a battery can do what the bike is exhibiting. If one or more of the pairs of cells become really unbalanced in voltage or the ability to produce power at the same rate as the other cells, then you could see the BMS crash the output as that pair of cells will go lower than 2.7 volts.

We had one of our guys weld up a pack without enough pressure on the welding tip, perfect looking spot welds but almost no contact between the Nickle strip and the cell. The battery worked really well until it got loaded up and then it would fail. Took me ages to find the fault as all the cells measured perfectly normal.

But both batteries, maybe if it was in a batch run but then you would have heard of others in the batch doing the same.

 

[Seraye]

Thanks for your feedback - I will be changing the contacts to spark resistance xt90’s, it is strange that this is happening to both batteries - and maybe it was a bad run- I contacted the seller (a well-known reputable North American dealer) but they have not responded to my inquiries yet. I have tried the disconnect and reconnect method to reset - but it won’t work - will not turn on unless it is charging/has been charged up. I am kind of just shrugging my shoulders and resigning myself to the fact that this will be my “only short errands around town bike” (hesitate to buy another battery from same dealer)

 

[Seraye]

Actually - I just tested one of the mini-cubes on a different motor - a TSDZ2 (almost forgot
About this one!) and the battery cut
Out on that motor Too! So- the issue must be the batteries!

 

[Waynemarlow]

- will not turn on unless it is charging/has been charged up.

Ah that’s the clue we needed. The BMS is shutting down the battery, most will only reset if you add voltage on the charge connector. So you have one or more groups of cells which has got way out kilter with the rest of the groups. Pretty easy to check with a voltmeter and locate which group is causing the problem.

The cells will only be out of kilter if they are a group of faulty cell / cells, the battery has never been fully charged on a successive number of times ( cell voltage never gets high enough to trigger the balancing of the cells ) or there is a high resistance connection between groups.

You may want to research how to “ top balance “ the cells as it’s an easy enough process. Almost certainly it would be worthwhile getting an expert to have a look if you don’t fancy opening the pack , as in all probability the two packs could be saved.

 

[Seraye]

Hi Wayne! And Neeko! Thank you for your feedback. I did some more internet searching and found an article that indicated my batteries might not have smart BMS’s… (?) so not sure if I can top balance? But whatever the case - I decided to purchase a new battery (more watt hours with a smart BMS) and I will turn this into an opportunity to learn how to repair (or build?) a battery.

 

[Waynemarlow]

Smart means something quite different. Smart usually means it has Bluetooth on board and you can use an App to view all the parameters of the battery.

You need to research "top balance" and generally how to approach poking around in Li-ion batteries, they can be quite dangerous to you health if approached wrong.

 

[Seraye]

Thank you - Absolutely will be researching - I have a lot of mechanical skills but very minimal understanding of electricity/ batteries. At least I won’t be in a hurry now that I have a replacement battery on the way.

 

[randycpu]

I agree that your pack could be un-balanced. The way you are charging your batteries could be the issue, combined with the design of these small packs (13S2P).
You said: "I am very diligent about charging them to 80 or 90% if not in use." Only charging the pack to 90% is a great strategy to maintain the cycle life of the pack. BUT, most BMS's will only balance the pack when a serial group reaches 4.20 volts. When you only charge to 80 or 90% of capacity, your pack is NOT getting balanced (see below).
Now let's talk about the design of the pack: A 13S2P pack has only 2 batteries in parallel for each of the 13 serial groups. Battery cells all exhibit unique behaviors. With only 2 cells in parallel, each cell is stressed more than in a larger pack that "averages" the unique behavior across the more typical 5 or 6 cells (6 X 2.3AH = 14AH).

Here's a primer on the most common balancing methodology for those battery users who are not battery pack designers: When the first serial group reaches 4.20 volts, the BMS applies "resistance" to keep that group from going over 4.20, which would be OVERcharging. As other serial groups reach 4.20 volts, they get the resistance treatment, in turn. Eventually, the pack reaches its max voltage (4.20 X 13 = 54.6 for a 48 volt pack), and the BMS shuts down the charging port. None of this happens until the first serial group reaches 4.20. There are other balancing methods that can be performed at SOC of less than 100%, and the more expensive BMS's can do these methods. If you build your own pack you can expose the balancing leads to control and monitor the process.

Conclusion: Maximum pack cycle life is achieved by limiting State of Charge (SOC) to 80 to 90%. But you must charge to 100% to get balancing. It's a delicate balancing act. [See what I did there?]

 

[randycpu]

Here's my second post on your problem:
Let's look at the (great) data you collected:
1 - In the first dataset, your pack voltage drops out completely after a relatively short, mild rise in load current (from 4 to 6 amps). The pack voltage droops about 250mV as the load increases and then the voltage crashes.
To me, if this data is correct, the data shows that the pack (really the BMS) is the culprit. The BMS has shut down (for whatever reason). If the motor controller was the one that cut out, the supply voltage would have spiked up as the controller FETs all turned off (because no more load).

2 - The state of charge algorithm of your motor controller (Battery %) is a bit off for the Samsung 30Q cell. Your data shows that the SOC is ~72% when the pack voltage is about 49 volts. 49 / 13 = 3.77 volts per cell. At that voltage, the 30Q has about 57% capacity. So your "Battery %" display is optimistic.

 

[randycpu]

You may want to put a diagnostic logger in line ( they are not expensive

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and see if the voltage is falling off significantly enough to trip the BMS. Do power the logger with a small battery though as they have no backup memory battery.

I’m not sure of the makeup of the battery but unless the cells are selected wisely you can run into problems with voltage fall off of even batteries at 70%. Try setting the max amps to say 10 amps and see if that changes things as I suspect 18 amps is quite a big draw off if you are reaching that sort of level.

But without knowing exactly the problem by using a logger of some kind, you are just firing off theories.

As you said, these loggers are very useful until the battery voltage drops out. At that point, you lose everything.
How do you power the logger from a second battery? Mine runs off of the main battery, as it is in series between the battery and motor controller.

 

[Waynemarlow]

As you said, these loggers are very useful until the battery voltage drops out. At that point, you lose everything.
How do you power the logger from a second battery? Mine runs off of the main battery, as it is in series between the battery and motor controller.

There’s a second connector which you connect something like a Pp3 to. Depends on the unit but do check what voltage you can apply to this connector but the one I use is happy to 15 volts.

 

[Waynemarlow]

Here's my second post on your problem:
Let's look at the (great) data you collected:
1 - In the first dataset, your pack voltage drops out completely after a relatively short, mild rise in load current (from 4 to 6 amps). The pack voltage droops about 250mV as the load increases and then the voltage crashes.
To me, if this data is correct, the data shows that the pack (really the BMS) is the culprit. The BMS has shut down (for whatever reason). If the motor controller was the one that cut out, the supply voltage would have spiked up as the controller FETs all turned off (because no more load).

2 - The state of charge algorithm of your motor controller (Battery %) is a bit off for the Samsung 30Q cell. Your data shows that the SOC is ~72% when the pack voltage is about 49 volts. 49 / 13 = 3.77 volts per cell. At that voltage, the 30Q has about 57% capacity. So your "Battery %" display is optimistic.

Randy think along the lines of just one group of cells has a very low voltage in comparison to the other groups. The total voltage of the 12 other groups will mask this group and the motor controller seeing the voltage level of the 12 groups, will be almost correct.

However as soon as the motor draws current, as the cells are in series, the power will be drawn equally across all 13 groups irrelevant of what voltage each group is at. If the lowest voltage cell has only charged 30% then the whole pack has only 30% of useable power, even though the voltage level of the entire group may indicate otherwise.

I‘m not sure that a BMS will act in the way you describe, my understanding is that a BMS looks for the first cell to get near 4.2volts and will shut down the total charge current to a low value. The charger that comes with most EBikes are not intelligent chargers, just simple 2 wire units that only read voltage and has no say which cell needs additional charge. Within the BMS is a resistor mounted on a heat sink. In this highest voltage group the charge current to this group is less than the current being drawn by the resistor and the energy is wasted via heat through the heat sink. The remaining cells continue to charge at a less rate. Now the charger senses that voltage is near the upper limit, the amps drawn is low, it shuts down to what we call a balancing charge but in fact is just a tiny amperage near the upper voltage limit. Most chargers will shut down totally at this point after a time limit.

Now the BMS gets really to work balancing the cells by applying the resistor on each cell, wasting the energy via heat on the heat sink, until all groups are now at the lowest voltage of the lowest group. But here’s the problem, our batteries are pretty high density high total Watts and if the BMS has to limit the temperature of the heatsink then it can only bleed off energy very slowly. In our cases it could takes months.

If a group of cells still is below the others when we come to use the battery next then it’s charge level is the one which controls the BMS’s low level shut off. Eventually you get into the situation of the OP where one cell group is way out of kilter. How do we solve this problem. Intelligent chargers that have a direct connection to each cell group and charges each group rather than a simple 2 wire set up. There’s a new breed of charger coming along as well which has microprocessor control via a 4 wire charge port that talks to an intelligent BMS that individually charges groups within the pack. All these microprocessors and wires cost money, would we be prepared to pay for this?

 

[Seraye]

As you said, these loggers are very useful until the battery voltage drops out. At that point, you lose everything.
How do you power the logger from a second battery? Mine runs off of the main battery, as it is in series between the battery and motor controller.

I agree that your pack could be un-balanced. The way you are charging your batteries could be the issue, combined with the design of these small packs (13S2P).
You said: "I am very diligent about charging them to 80 or 90% if not in use." Only charging the pack to 90% is a great strategy to maintain the cycle life of the pack. BUT, most BMS's will only balance the pack when a serial group reaches 4.20 volts. When you only charge to 80 or 90% of capacity, your pack is NOT getting balanced (see below).
Now let's talk about the design of the pack: A 13S2P pack has only 2 batteries in parallel for each of the 13 serial groups. Battery cells all exhibit unique behaviors. With only 2 cells in parallel, each cell is stressed more than in a larger pack that "averages" the unique behavior across the more typical 5 or 6 cells (6 X 2.3AH = 14AH).

Here's a primer on the most common balancing methodology for those battery users who are not battery pack designers: When the first serial group reaches 4.20 volts, the BMS applies "resistance" to keep that group from going over 4.20, which would be OVERcharging. As other serial groups reach 4.20 volts, they get the resistance treatment, in turn. Eventually, the pack reaches its max voltage (4.20 X 13 = 54.6 for a 48 volt pack), and the BMS shuts down the charging port. None of this happens until the first serial group reaches 4.20. There are other balancing methods that can be performed at SOC of less than 100%, and the more expensive BMS's can do these methods. If you build your own pack you can expose the balancing leads to control and monitor the process.

Conclusion: Maximum pack cycle life is achieved by limiting State of Charge (SOC) to 80 to 90%. But you must charge to 100% to get balancing. It's a delicate balancing act. [See what I did there?]

Wow! Thank you for that great feedback! I did purchase another larger capacity battery to use while I figure out if these batteries can be revived somehow either through balancing ( charges to full) or repair.

 

[randycpu]

Randy think along the lines of just one group of cells has a very low voltage in comparison to the other groups. The total voltage of the 12 other groups will mask this group and the motor controller seeing the voltage level of the 12 groups, will be almost correct.

However as soon as the motor draws current, as the cells are in series, the power will be drawn equally across all 13 groups irrelevant of what voltage each group is at. If the lowest voltage cell has only charged 30% then the whole pack has only 30% of useable power, even though the voltage level of the entire group may indicate otherwise.

I‘m not sure that a BMS will act in the way you describe, my understanding is that a BMS looks for the first cell to get near 4.2volts and will shut down the total charge current to a low value. The charger that comes with most EBikes are not intelligent chargers, just simple 2 wire units that only read voltage and has no say which cell needs additional charge. Within the BMS is a resistor mounted on a heat sink. In this highest voltage group the charge current to this group is less than the current being drawn by the resistor and the energy is wasted via heat through the heat sink. The remaining cells continue to charge at a less rate. Now the charger senses that voltage is near the upper limit, the amps drawn is low, it shuts down to what we call a balancing charge but in fact is just a tiny amperage near the upper voltage limit. Most chargers will shut down totally at this point after a time limit.

Now the BMS gets really to work balancing the cells by applying the resistor on each cell, wasting the energy via heat on the heat sink, until all groups are now at the lowest voltage of the lowest group. But here’s the problem, our batteries are pretty high density high total Watts and if the BMS has to limit the temperature of the heatsink then it can only bleed off energy very slowly. In our cases it could takes months.

If a group of cells still is below the others when we come to use the battery next then it’s charge level is the one which controls the BMS’s low level shut off. Eventually you get into the situation of the OP where one cell group is way out of kilter. How do we solve this problem. Intelligent chargers that have a direct connection to each cell group and charges each group rather than a simple 2 wire set up. There’s a new breed of charger coming along as well which has microprocessor control via a 4 wire charge port that talks to an intelligent BMS that individually charges groups within the pack. All these microprocessors and wires cost money, would we be prepared to pay for this?

Yes, I agree with all you have said. Both packs are likely way out of balance. I suggest several cycles of charging to 100% and discharge to shutdown. If that doesn't work the pack would have to be torn down to expose the balancing wires currently connected to the BMS.

What we should be working on (advocating with our wallet) is a change to the balancing "algorithm" that allows balancing at lower top voltages. This would require a redesign of the BMSs, but with no additional components (so same BOM cost).

 

[Waynemarlow]

What we should be working on (advocating with our wallet) is a change to the balancing "algorithm" that allows balancing at lower top voltages. This would require a redesign of the BMSs, but with no additional components (so same BOM cost).

I think some of the more expensive Bluetooth capable BMS's already have this function. But it would only be a working solution if the chargers also " talk" to the BMS.

Sadly for us and our battery packs, for a few extra dollars in components in the initial design of both the charger and the BMS, that is not going to happen anytime soon. Until then simply fully charge to 100% guys every time, yes it may shorten the lives of the battery by a small number of cycles, but will you ever do 3000 - 4000 charges that a Lithium cell can do with ease.

 

[Tr3vor]

Hello,
I am having an issue with My BBS02 cutting out when my 48v mini cube battery reaches around 70% (about 50/51v). I have two mini cubes and this happens to both batteries, and ALWAYS at that level. I am very conservative with my power usage - I like to pedal and do not have a throttle, have my controller limited to 18 amps and I am a “spinner.” The power has cut out at all times in a flat mellow stretch of the ride.
I checked all connections - there is no visible damage at any of the connections and there are no loose connections, I use the EggRider display, and I even changed out the Motor controller (with a lunacycles improved controller) just in case.
As far as my batteries are concerned- I am very diligent about charging them to 80 or 90% if not in use (tho they are used every week if not daily- even in the winter) I have rarely drained them below 50% and I have never completely drained them. I always slow charge them (1 or 2 amp charge) and I Purchased an advanced charger that shows voltage - in the hopes of balancing the batteries - tho this does not appear to work (the charger cuts around 53-54 volts then turns off and will not come on again). I also bring my batteries inside if it is going to dip to freezing or colder (rare here).
Last detail - I use Anderson pole connectors.
—- so, I have searched the web far And wide for an answer to this issue- I have found numerous postings by individuals with the exact same
Problem - A power cut at about 70% this problem seems to always involve a bafang motor (searched for tsdz2 and found no posts about this problem) and happens with different types of batteries - 52v as well as 48volt. I have seen advice on steps to problem solve this issue - but all these feeds end without any real solution.
Oh - and some other details - these batteries worked are almost new - I have done numerous rides with no problem. One battery is more lightly used - probably not even 100 miles on it- the other battery has only about 300 miles on it - if that means anything.

And lastly - I have my set my controller to cut off at 39V.

:
1. Has anyone here had a definite solution to this problem? A solution that is tried and true for hundreds of miles?

2. Can anyone tell me if my Mini cubes have a BMS? Excuse my ignorance, I am learning here, but this is an issue with both of these batteries. I am a bit dismayed because they have so few miles on them and I purchased them last year (I think last year) . I have tried to balance them with my new charger but that doesn’t happen - I have turned off the charger let it sit for an hour then turned it on to top it off - I have done this over the course of a day - the battery approaches 54.4ish… but problem still occurs.

3 is it possible that I have damaged the bms of my batteries with too much disconnecting/reconnecting with the Anderson pole Connectors ? I do sometimes hear the spark and have only disconnected my batteries mybe half a dozen times now - I have ordered xt90 spark resistant connectors to avoid this.

I am dismayed that this is happening so early on- with fairly new and not abused parts. If the solution is purchasing a new battery - so be it - i’d like to have reliable battery power for
More than just a around town trips.

this seems to be a bafang issue andthe posts I’ve found about it have exactly the same issue if the battery cutting at 70%ish. I would appreciate any recommendations or information or anecdotes you might have about this issue.

And Please share if this is your experience.

Hi there! I realize this post is 2 years old but I'm experiencing the same issue.... Not sure if you still use this account or if you will even get this message but ... Were you able to resolve it ? Or figure out what the issue was that you were having with the battery shutting off around 70%? I signed up just to ask lol thanks in advance cheers!!!

 

[Seraye]

Hello!
Yes, the problem was resolved. It was the battery, not the Bafang motor. Those mini-cubes are junk, they work for a while, but get unbalanced. Get a quality battery, like something from EM3EV with a Smart BMS system that balances the charge level of the cells. I have had no problem with the Shark batteries purchased through EM3EV.

 

[Tr3vor]

Yeah the battery that I have is the one that came with the bike it's an expensive one I'm pretty sure it's actually my friend's bike but he paid like $2000 for it and he only drove it for one season I told him it sounds like a loose connection or something then he told me that he rode the bike over a jump so
Could that make a cell un balanced or he probably just knocked something loose soon as he brings it over I'm going to open it up and check it out. When you say cube batteries are you talking about the Alibaba style ones that say like 60,000ah online wrapped in blue plastic?

 

[Seraye]

Hello, The mini-cube was purchased from a reputable U.S retailer that guaranteed the quality of the battery cells. I won't name the retailer, because I do believe they are honest people to work with, and I noticed that they no are no longer selling these mini-cubes. I bought two, and both had the same problem. I was new to DIY ebike kits at the time and had no idea what to look for. I would not know if these mini-cubes sold by reputable local dealers are the same as the mini-cubes sold by Alibaba, but I personally would never ever purchase any battery from Alibaba (or Amazon). I have since purchased two batteries from em3ev with smart BMS that balance the cells, and have had absolutely no problems with these batteries at about 2000 miles of use. As for your question regarding whether something came lose in your battery, I would have no idea if that would make a battery become unbalanced as I have very limited technical understanding of batteries.

 

[randycpu]

Yeah the battery that I have is the one that came with the bike it's an expensive one I'm pretty sure it's actually my friend's bike but he paid like $2000 for it and he only drove it for one season I told him it sounds like a loose connection or something then he told me that he rode the bike over a jump so
Could that make a cell un balanced or he probably just knocked something loose soon as he brings it over I'm going to open it up and check it out. When you say cube batteries are you talking about the Alibaba style ones that say like 60,000ah online wrapped in blue plastic?

Batteries are not really mechanical, so it is VERY unlikely that jumping type riding would cause an OEM battery to become unbalanced. Even a bad crash.
The more likely cause is an electrical component failure internal to the battery pack. Either a cell went high impedance or a component in the BMS failed.
Did they get the bike / battery wet? THIS would do it.
The battery either needs to be replaced with an OEM replacement part or repaired by a skilled battery technician.

 

[Astro66]

I have built 3 BBS02 ebikes. You need a 48V 15Ahr battery as a minimum, IMO. I have used 10Ahr batteries. But find the individual battery cells get too hot, and fail quickly. So whilst the battery charges and works. It stops working after a very short distance.

I have used a 10Ahr pack. But it used Panasonic Cells. Panasonic, Samsung and LG cells seem to tolerate higher loads better.

My advice has always been. Don't skimp on the battery. It will always cost you more in end.