Hi @SteveCook
I’ve got a plant system with 2x Gen3 5.0’s and 2x 9.5’s on each inverter.
Although our inverters are different Gen’s I think you’ll likely see similar battery behaviour that I see on each inverter and battery pair individually.
I had a hell of a lot of issues in the beginning at install time (search my earlier posts); Mostly due to issues with faulty batteries (cells within a battery). I’ve had 3 of the 4 replaced - which took about 18 months of back and forth with support to eventually get sorted. The original one is still a bit “iffy” but they won’t replace it as “it’s ok”, - their words, not mine !
Now, each battery pair is kept pretty tightly balanced in terms of voltages. But the SOC does creep apart and will display a different percentage for the same voltage for some weird reason. You just have to get used to that. 10-20% is common, although it’s usually 5-10% ish.
I think this issue is likely due to the calibration, some quirk in the BMS, different mapping scales used for each battery, the variance of the cells, total capacity variance in a single battery or whatever else. I think they probably operate normally, it’s just the SOC numbers for a pair are, shall we say “non optimal”.
During a calibration of a pair (or tripples, I assume) they both get discharged and charged (calibrated) at the same time. I think somehow this skews the 0-100% usable “range” (because of the whole range being different(?) ) and hence you see different SOC at different times from this “fixed” (by a calibration) ‘usable’ range. Maybe the results would be different if you could calibrate each battery separately…?
The good news is that I do pretty much get the full usable capacity out of a pair. So you should too. If the Gen1 performs similar to the Gen3 then what happens on mine is this….
A) You’ll likely see the primary get hotter and “move” more than the secondary under load.
B) At the extreme high or low SOC, if left long enough, the secondary will catch up (partly) if it has time (in terms of SOC - voltage should be similar (or not !!); within 0.1 or 0.2v).
C) At lower rates of charge/ discharge they seem to be slightly better at SOC staying together. Especially if it’s a combination of slower charging and discharging (ie in the day) Although not always.
One battery pair on one inverter appears to keep the SOC much closer than the other pair, although there is a split on that pair as well.
The Gen 1 has a lower charge/ discharge rate, so you might not see as bad a SOC split as what I’m seeing. You may get a closer SOC all the time.
Long and short of it is that I am able to pretty much use the whole capacity of both batteries on an inverter.
Also, FWIW, I think best advice is to put the new battery as the primary NOT the secondary.
