Battery discharging

[rbk]

This is on my newest ‘other’ boat and not on my cruising boat, a custom aluminum jet boat. Found out right away the corrosion in the cable off the battery switch engine as causing too much resistance and it wouldn’t start the engine or power the trim motor. Replaced the switch, threw in a blue seas ACR wired proper for x2 - 12V (start/house) real basic stuff. The start battery was low (assumed they PO wired the ignition hot and drawing the battery down). Bought a relatively smrt charger and hooked it up (after wiring in the ACR). Thought I’d combine the two banks in order to bump the low batt to trick the charger but it threw a reverse polarity code. Separated the banks and put the charger into ‘repair’ mode to get it to charge it. Morning comes and the battery is charged; unhooked and left for the day. Come back and it’s 10.5v. I came to the conclusion the battery has a bad cell but would that cause a reverse polarity when combining the batteries? Or some other issue? Lots of power boats wired with ACR’s like this and shore charges not throwing RP codes?