New 6v house batteries & main battery losing charge

Let me ask you a question. Once your batteries have been on the charger overnight and then you remove the charger.....exactly what are you expecting the voltage to be on the batteries?

Charging voltage is different from the battery voltage. You can't expect the batteries (once charged) to stay at the charging voltage rate. They will automatically drop down to their "full charge state" which is 12.6 to 12.8 volts.

I think you are making much to do about nothing.

Ron