What’s the procedure for replacing a single “bad” battery in a bank of batteries with a few years on them? Looks like a good opportunity to create a significant imbalance.
If you install a “new” battery into a string of older batteries, you can be sure it will immediately “assume” the charging capacity of the rest of the string since they will determine the charging voltage and charging current. In other words, after a few weeks of charge/discharge cycling it will act like its the same age as the other batteries.
I have replaced a bad battery in a string that was less than a year old with good results, but think it would be a waste of money to do this for an older battery bank, as its best to replace all at the same time. A battery bank is just like a chain, its only as good as the weakest link.