Only charging to 99%

So a little over a week ago I got a second battery, thanks @JacoDeJongh

Old battery is a 100Ah bsl battery about a year and bit old.
2nd one is 104Ah as 100Ah discontinued.

When I used the new battery bms as primary it sets the voltage to 55V via bms and the battery did get to 100%, however after the out of the blue feeding back to the grid I tried to revert all my chages to watch what it does and change things slowly and in doing so I reverted to old bms, this one though sets the chage voltage to 54.5V and the battery doesnt get over 99% (maybe for 2min randomly gets to 100% then drops again)
Also old bms reports 200Ah and new reports 208Ah.

Any suggestions? although out the country so will only test changes when back.

Only thing I note is that 1 cell 2::6 in new pack only gets to 3.38 which might ne holding it back.

I would ignore it. At least while I am out of the country.

SOC is an estimate anyway, and most (if not all) BMSes simply reset to 100% when the voltage spikes up (either the total voltage, or that of the highest cell).

SOC drift is also something that happens, because the current measurements in- and out of the battery always have a small measurement error, and that is why the BMS needs to occasionally reset, which it does when the voltage spikes upwards. Since a voltage of 3.45V or more per cell (whatever the BMS targets) is a physical property of a LiFePO4 cell that is pretty hard to argue with, that is what they use.

A BMS that doesn’t reset to 100% means it’s a couple hundred mV low and the BMS isn’t seeing the trigger. But the fact that it counted up to 99% just using it’s shunt/hall sensor or whatever it uses means the battery is properly charged and there will be no damage.

Check your minimum and maximum cell voltages as well (I think BSL sends those?). If the lowest cell isn’t badly undercharged (under 3.35V) I would not worry. The SOC estimate is out by 1%. Pffft.

This. :smile:

The biggest issue is if the SoC starts to drift, but the BSL seems to handle that well (it drifts up). As long as it reaches 100% now and then, you are fine. I would have put the new battery as the master, as you had it before, but it’s not that important. The values reported to the inverter is double the settings of the master, but having it report 208Ah instead of 204 is not a big deal, the SoC% should still be accurate.