I had an issue recently with soc drifting. One out of six batteries was showing only 78ah stored, with total capacity at 99.8ah. The low battery was at th3 same voltage as the high batteries. I disconnected all but the low battery, and ran some big loads on my system. Battery showed 0% soc at...51.5v I think. I kept the (30-60a) loads going until voltage dropped to 48v. As it recharged, the soc was more in line with it's brothers.
I want to point out that I charged the single battery up to 51v, then turned on the other (54v) batteries, one at a time, while monitoring the low battery with a clamp meter, and I never saw more than 30a going into the low battery. Doing this is usually recommended against, but I wanted to see what would happen. No bangs, no smoke,
Figuring the rest of the batteries might have drifted, I brought the whole bank down to 48v over the last few days, and am (slowly) recharging back to full. Despite the weather reports, the clouds moved in
I want to point out, my house idles between 200-400w, which might be too low of a draw for the batteries to register, leading to this soc drift. They usually are charged to 100% every day (55.6v 1.5hr absorb for balancing, float at 54.0v), and almost never drain below 75%.