I have been working with two 12 V lead-acid batteries in series. Accidently, we kept them turned on for a day or two and one of them drained to ~3 V and the other to ~8 V.
I immediately charged them, but they get charged and drained super quickly. I read about recovery charge on this forum, but my charger doesn't seem to have a recovery charge function.
Also, sometimes it gets charged to 16 V on balance charge. Can those batteries be recovered or should I replace them?