180mV imbalance at 13% SoC

I have 16 EVE LK280 Grade A which I had top balanced about a month ago; they are normally all at the same voltage at high state of charge, but a couple of times I took them close to 10% SoC (which is as much as my inverter would let me) and noticed a 180-190mV imbalance with a 8A load; the imbalance stays the same (maybe drop to 189mV) if I remove the load
Is this to be expected?

The big question is do they balance back up when you charge the battery? Most BMS's balance cells while charging only.

Rednecktek said:

The big question is do they balance back up when you charge the battery? Most BMS's balance cells while charging only.

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Yes

Then I wouldn't worry about it too much. It's not all that uncommon for cells to drift a bit as long as the balancer is working when you fill it back up.

Rednecktek said:

Then I wouldn't worry about it too much. It's not all that uncommon for cells to drift a bit as long as the balancer is working when you fill it back up.

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The problem is that the low cell triggers the undervoltage protection so I don’t get to use all the energy in the battery
One cell could be at my low voltage cut off of 2.7, when most of the others are at 2.9V
This happened at 13%

Unless you want to go through the hassle of doing a bottom balance I think you're not too bad off. Even then a bottom balance probably won't do you that much good. Most factory LFP batteries cut themselves off at 10% anyways so you're still "within norms".

Grab yourself a good active balancer and throw it on the pack. That should work on balancing the cells as they go down so they hit the bottom end together without relying on just the charging balancing. Fortunately from what I've seen having a second active balancer and your BMS balancing at the same time doesn't hurt anything, it just helps control the runners faster.

That should help even out your voltages as you discharge and get you that last few % you're wanting, plus if you've already built a battery it's going to be super easy to throw a balancer on there. It's the same as the BMS wire harness, it just plugs into a smaller box.

Reconsider the 13% SOC, at 2.9 volts the true SOC will be at the most 7 or 8% SOC.
Since the inverter cuts off , as it should, at low battery volts to protect the battery, why is it a problem?
If you mess with the balance at the bottom then you will lose the top balance.
Pulling the battery down below 10% SOC is considered to reduce battery life.
Adding an active ballance to function throughout the working range may not resolve the issue.
You have cells of slightly different capacity, they may be so called grade A, but won't have exactly the same capacity. Its the weakest cell that determines the battery capacity.
Providing the battery is inbalance at full charge, I suggest you stop worrying.