Boondocking - do my batteries need to be replaced?

[QZ]

IIRC you are testing the load across the terminals you are connected to, not the bank.

If you put the load tester cables on battery one you are still drawing on battery two because they are connected together. When two 12's are in parallel they must be disconnected for testing.  That's why they both go down at the same rate when using them. When testing sixes connected in series you can move the test leads from battery to battery and you will only be testing the battery that you are connected to.