SOLAX the manufacturer I believe are completely setup to say everything is working no matter what you say to them, however, I did have an interesting email from SOLAX saying that all the cells were showing the same voltage.
I replied to ask for a screenshot since no one else can see that data.
It would be good to see as it kind of eliminates the rogue cell theory.
Depends on the voltage of the cells at the time, on 3.65v cells like I use you will get more drift at the top end, and I should think its the same for cells that operate at other voltages. On my system , one battery BMS shows 30% SOC, the other 25% SOC, Victron shows 27%. All three are calculated/tracked independently of each other. Any way, each battery has a maximum cell difference of 0.003v at this moment in time, but as you charge the batteries that will drift and get bigger, which is why we balance the cells above a certain voltage.
Its when the cells get full that you get cell voltage imbalance, and therefore problems. Think of sixteen milk cartons as the 16 cells, they all hold two litres of fluid, they all fill at the same rate, when one is full it flicks a switch and they all stop filling up, now squash one, its going to overflow before its taken 2 ltrs of fluid and thus fill up quicker than the others, and thats what happens with a cell, once it gets full, its voltage rises quicker than the others, so unless they checked the cell voltages at the very top end the figures are worthless.
I also think its very hard to get quoted power out of batteries, mine are 14.5kWh each, but I'll never get that as I don't run the cells from 3.65v down to 2.5v, which should give 14.5kWh of energy, but that does depend on cell quality. In fact I've never bothered test capacity, not even of a single cell even though I bought a test rig, just never got around to it.
One would hope though, that a manufacture when advertising a ready built domestic battery, has got their sums pretty close.