when paring batteries,match is critical.
our campground runs a 20kw diesel generator,an inverter and 3 banks of 6 volt batteries series wired making 24 volts.
if any one of the batteries gets weak,it pulls the entire system down,forcing generator to cycle frequently.
2 volts difference between best and worst battery is enough to cause problems.
if running a 12 volt system,and choosing to run 12 volts in series circuits,i reccomend no more than 100 amp cranking power difference.
keeping battery type and amperage matched will make the system much more efficient.