If batteries of a bank are wired as two in series, then voltage between the two could give some info about which one of the two is in a worse state.
Example: If the whole bank drops to 24volt, and all the mid-voltages are ~12volt, then there is no ballancing problem.
If one mid-voltage of the bank shows 11.5volt or 12.5volt, then there is something wrong with that set.
This is basically the same as measuring individual cells in a pack, only now with batteries of a bank.
INA219 breakout boards could be used to measure all those mid-voltages,
AND the charge/discharge currents of the sets across shunts between the two batteries.
Leo..