I used a 4200mAh LiFePO for a couple of activations and put it on charge on a B6AC charger. I gave it a balanced charge with the current set for 1A max. Everything looked completely normal and checking during the charge showed the cell voltages were close to each other. I thought nothing more and it stopped charging after a while. Fine so far.
When I checked each cell before disconnecting, three cells showed about 3.55V and one showed 3.3V. I’ve never seen one cell drop below the others like that before. Thinking about whether the cell was weak I did a discharge cycle. Within a few minutes all cells were about 3.3V and the discharge cycle was still happily working at 0.4A 90mins later. All the cells seemed to be close in voltage. So it looks like the battery still works fine.
I put in on charge and when I came to look at later one cell was at 3.6V and all the others were around 3.37V and the charge current was down to 0.1A. I wondered if the charger was failing so I stopped and put another LiFePO on chrage and that behaved as I expected. So back tothe first cell and within a minute it was back to 0.1A charge, one cell at 3.6V the other three at around 3.38V. So I left it charging and 50mins later I heard the end of charge tones and came and checked. All cells at 3.5-3.6V.
Anyway this morning it’s back to 3 cells showing around 3.6, 3.57, 3.54 and the fourth showing 3.39, same cell at a lower voltage as before.
Is this “normal” behaviour? All the years of using LiPo, LiFePo use, I have seen the cells in the batteries closely matched and never had one behave like this. Or is this common and I should stop worrying?