What to do when one cell voltage far below others

Hi all

I’m a noob to Esk8ing and have come across my first battery issue.

One of my cells on one of my 2 6s batteries is about 1V lower than the others. My charger has given me the warning “balancer voltage too low”. When I checked, the voltage was 2.538V while the others where ranging from 3.19V to 3.60V (See the attached images)

Is the situation irreversible? I’ve read the anything below 3V is pretty bad for lipos so getting this low is probably going to mean I throw away the pack. Also, the fact that there are such major differences between the voltages doesn’t seem good either.

To give some context which might help - I rode my board today (Trampa Urban Carver, 136kVa motor) with the batteries at around 55%. They are connected as 12s. I had charged the batteries about 4 days ago and then rode until about 60% on that day. My ride today was really short - 3,3kms on relatively flat road, but the battery went to 7% at the end, which took me about 25 minutes. It was when I tried to charge the batteries again to storage levels that I got the warning.

I’ve checked the other battery and everything there looks good and all values are within a hairs breadth of each other.

Any help here would be greatly appreciated.




Does it show and external signs of stress? Puffing? Leaking?

If not, you might be able to charge it up and balance just fine

Just keep an eye on it and a bag of sand near by

Thanks for the advice, Sn4pz. I can’t see any visible issues at all.

I have a Lipo bag that I’ll use when trying to charge it.

The charger won’t allow me to even charge it using the balancing cables when sees a voltage below 2.75V but the manual recommends charging it without the balancer cables for a few minutes to get it above the threshold and then continuing with the balancer cables after that.

All your cells are pretty much out of balance. That doesn’t look good at all. Usually the cells should be around ±0.1V from each other. Did you already tried something in the meanwhile?

Something else that may have impacted this is that I didn’t prep the batteries before I used them for the first time about a month ago. I just connected them to the board and used them. They ran to 0% (as indicated on the led indicator on my board) and when I then connected them to the charger all the cells were at around 2,98 - 3.02ish. They charged and balanced fine immediately after that, but perhaps that wasn’t the wisest thing to do with new batteries?

I must admit that it’s exciting to learn about how all of this works (the electronic side of Esk8ing) but it’s also a little scary, because it’s not a cheap endeavour (at least not here in a South Africa) and not ruining my equipment is definitely high on my priority list!

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No, I haven’t tried anything yet. I’ve been waiting for advice from this forum.

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The battery is in general over discharged. Probably no permanent damage if its the first time but deff dont make it a habit.

You can charge without balance wires until the last cell reaches 3.2v then charge normally.

The reason all the cells look so out of balance is that you over discharged them. Once batteries reach 3.3v they can drop down to 2v in matter of minutes.

Charge your battery and balance them. After ride until you see about 3.5v/cell under load or 3.7v/cell with no load. This should be your new 0% charge. Keep it above that and your battery will last a long time.


What capacity is your battery? Charge it at 0.2x the capacity in current as soon as possible. The longer you leave it over discharged the more damage there is.

Also try to keep the battery compressed and cool when charging initially to 3.2v min. That way it wont delaminate.

If you make this a habit then your batteries will die very quickly.


Its 2x 6s 6000mAh in series, so 12s.

So I connect the one battery to the charger without the balancing cable and charge for a few minutes. I then put the balancer cable back in and check the voltage of the lowest cell to see if it’s above the threshold of the charger’s minimum allowed voltage. Once it’s above that I leave the balancer cable in and continue to fully charge it?

I guess I should also change my LED indicator to show Volts, not percentage?

This happened yesterday afternoon (about 12 hours ago) and I was too scared to do anything about it until I’d asked here.

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Correct. You should charge at 1A initially. Also yes. Change to display voltage.

If you keep over discharging the battery like this. It won’t last very long at all.

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Thanks. I’m definitely going to try monitor things better from now on.

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I can recommend you to add a lipo alarm to your packs

it´s cheap and you can set your indication voltage how you want. so if any of your cells in your pack will drop down the set voltage you will get an alarm.

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Thanks Andy. What concerns me is that I’ve got the Vesc 6 and it’s supposed to have the battery protection checking in it. I’ve set all the thresholds correctly but it doesn’t seem to be accurate. I don’t know if it tracks individual cells though.

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The vesc6 like any other vescs only monitor the over all voltage. if you want to monitor the single cell voltage, you need a BMS for discharge, or the cell checker I linked you. What was your battery cut off start and cut off end setting in the VESC?

For lipos it should be something around 3.5V per cell, so for 12s for example cut off start at 44.4V and (3,7V per cell) and end at 42V (3.5V per cell)

I’ve got the cut off start at 44.4 and the end at 38.4, which is 3.2 per cell.

I’ll definitely take your advice and get a cell checker.

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3.2 is very low for lipos, that’s probably why they got overdischarged in the first place. You should set the cutoff end to 3.7 like @PXSS said.

rise the cut off end to 3.5V per cell. after that you anyhow don´t get something out of the packs and the risk is too high to overdischarge them, like you did. better save than sorry :wink:

EDIT: I noticed that the cell checker not super accurat, means they meassure the volatage ±0.2V depending on the one you get. I would recomment to check the cell voltage first time with your charger, thant with the cell checker and than adjust the alarm limit to the tolerance the checker has. Or just set the alarm a bit higher and you will get the peeping more early :wink:

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I think he is using lipos, I would definitely not recommend recharging after a cell has gone as low as 2.5v. This happened to me the other day and I have ruined my pack

Your lipos is trash. Replace it. Set your hard cutoff to 42v. Set you soft cutoff 44v. Try not to run it to hard cutoff. You’ll harm the lipos.

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