So the charge each other was a little fib. Example- my Duramax battery is not carrying load anymore. Repair is 2 new high quality batteries correct group size and amperage rating of at least what GM requires. Same size, same cca. Connected in parallel. Are you talking about multi battery power banks, backup power supply or dual battery trucks and dual alternators? " charging system will be based on weakest therefore thats your power level" ? Didn't you just say the charging system will keep trying to chargethe weaker battery resulting overcharging good batteries?
I think you’re trying to massively over complicate this. The OP is talking about dual alts/dual batts in a parallel system. I don’t know why there is talk of wiring in series and 24v systems as it is not what the OP is working with.
You’re also confusing battery voltage and amp loads. A battery can show 12.8v and be considered fully charged but have dead cells and carry a low amp load rating. You can have a 12.8v charge and on two different batteries, but one may be a faulty battery only produce 1 amp and the other is a working battery producing 800 amps. Both show good on a tester, but one will function under a load and the other won’t. That’s why you can’t just put 8 AA batteries together and start your car, even though it’ll read 12v.
Batteries will always want to equalize to the weakest battery in the system.