Sorry about the corss-post

Two identical RV batteries. They have been unhooked from the RV
'converter' (smart trickle charger) for 5 days. Checking with a hydrometer
shows that all cells are 75% charged. (12 cells, two batteries). HOWEVER
one of the batteries reads 12.35 volts while the other reads 8.6 volts. Why
this discrepancy when the hydrometer readings are identical? Obviously, I
will replace the low voltage battery, but, I want to learn why the
hydrometer readings are in discrepancy with the voltage readings. BTW,
checked the voltmeter against my truck battery (everyday use). It reads
13.2 volts with the engine not running.

Thanks for all replies,

Ivan Vegvary