T&T: Hot Battery

[Robin]

Your individual hot batteries ARE a mystery.

Sounds to me like the batteries are defective if they fail so early. AGM's are
sealed, right? Did West say they were getting other returns/failures? If the
charger voltage were wrong, you'd think all the batts would get hot...

Replacing a used battery with a new one in a bank should be ok as long as the
existing batteries are in good shape, as yours appear to be. An existing
battery(s)  which is a bit weak will just drag down a newer more fully charged
battery. But are AGM's especially sensitive in this way....I've never seen
that as an issue....and I don't know why they would fail one at a
time....strange...

As you probably know, the cable from the batteries to the inverter/charger has
nothing to do with your hot batteries...Even a  cable smaller than ideal would
just weaken inverter output (via input voltage loss) when load was high;most
any any cable would handle the charge currents and bring batts to full charge
voltage...

Here is a possible test: Some day, disconnect all the batts from the
string..let them sit a few days, then test voltage...see if the older ones are
lower than the new...and if one is lower, see if thats the next to get hot.
Just a tenth or two of voltage difference is significant..for lead acid, 12.5
is full and 12.2 is 50% charge ( no load)....

let us know what transpires,
good luck.