Battery Balance Queation

Hi guys

I built a 12s8p battery pack at the weekend using molicell 21700 cells from Fogstar. I am using the apex smart bms, seems to charge well but it seems to struggle to balance. What are some common reasons for this? The pack is spot welded using 0.2 x25mm nickel strip.


0.068 is a pretty high voltage delta, your BMS is gonna struggle to balance 8P anyway but if you can do a balance charge (Keep the pack on the charger for a few hours, monitoring it) that might help. If you notice group 10 keeps drifting high there could be an issue with its capacity but run balance and go through a few cycles first.

Also what are those round white circles with the B icons? Could that mean its only balancing those 3 groups?

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It wil switch every few seconds to other groups

Edit: if everything is fine that is

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I suppose its weird that its potentially trying to balance groups that are already balanced (Maybe that’s what it means)

I stopped using these bmss as the app disgusts me

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idk man i find the app just fine. and now that it can be paired to metr and soon davega, once it’s setup you really don’t need to play with the app


So you guys reckon just cycling the pack a few times? Yesterday before the ride it was balanced fine. But after I had taken it off charge group 9 was quite high but the BMS leveled it all out over night before my ride.

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Offtopic but what do you use then?




If it was fine, and in one cycle it is that far out of balance, something is definitely up with your pack.

If it were me i’d be inclined to keep using it/cycling a few times to see if the problem gets worse/better. There is likely a very large risk element with this approach.

The safe approach would be to thoroughly open and inspect every part of the pack in detail… that’s a whole lotta work, but it might save you from a disaster.


Just went through similar issue with fresh 12s4p pack with recycled 40T cells. Go to settings and disable ‘‘Charge balance’’, connect it and disconnect it from charger to apply the setting. That way it will balance pack even when charger is not connected. Secondly, charge it to full and let it sit for few days. In your instance with pack this big it will take about 4 days to balance to 0.015v delta. A good way to avoid such dis balance to a big pack is charging battery to full every time you charge it, that way battery will have better chance to balance out. Also since it’s new pack, do couple of full charger and discharges (drive it till it hits 3.1v per cell, then charge it to full again and repeat)

Couple of other things:
-After long ride, don’t instantly connect charger to pack, instead let it sit for few hours for battery to ‘‘calm down’’ (it’s chemistry after all) and then charge it.
-0.06V delta is not great but not terrible, I would start worrying above 0.1/0.2v delta. 0.4v delta is super bad.

Credits to @glyphiks and @poastoast and battery mooch for info.

Also, if possible, send screenshot of the settings, maybe there is something wrong there. The app is glitchy at times but it does the job. There aren’t that many smart bms’s arround sadly.


If possible, do a benchtest of your pack from full to empty SoC with intended contineous current.
This will give you a very good indication of your pack health, available capacity, voltage sag and even how much drop you have over the cables.

Building a pack and not testing it before going out is ludicrous


Balancing in the mid voltage range is kinda pointless and can make it take longer to balance properly at the top of the charge.

My comment above neglected the fact that this battery isn’t at full charge.

Try fully charging the battery and see how the balance looks then


In my instance LLT failed to even do it at top of the range with ‘‘charge balance’’ enabled. Once I disabled it did the good old ‘‘balance by dissipating energy through resistors’’ quite nicely. Took two days however. LLT is funky and sometimes doesn’t act like regular bms’s


Weird. I’ve never known an LLT to not balance.


Thanks for the detailed info RDs.
Attached is the screenshot of the settings. I will give it a nice.balance change tonight.

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Setting the target balance difference to low can mess things up in my experience. Your 0.03 should be alright.

There is no oversight this way, I know.
But in my time, this app was very very unreliable. I can also show you a fried one. Bad experiences… if I had an iphone i might have kept it, that app was a lot less “china”

I’ve seen more bestech bms fried than any other bms. I would go without a bms before I used one.