Batteries.

[Jon 360]

Immm

Maybe ours was f-ed as there was a voltage drop or .3 volts across it

Doesn't sound much but that's a big part of your charge when you think that 12.8 is a fully charged battery and 11.8 is flat

[too_tall 15]

Too_tall - although I understand why that seems good, there isn't really any benefit, but there area few down sides. Firstly, there's no harm in the VSR staying on for a bit after turning the engine off. It won't allow your start bank discharged much by house loads at all, and typically it will turn off quickly, or once a load is switched on for very healthy batteries. Secondly, if you have other types of charging, shore, solar etc, the VSR won't turn on to charge the other bank while these things are charging, but the ign is off.

I was not thinking of alternate charging systems. Our shore charger has 3 isolated outputs which negates the need for the DVSR to remain connected. What I have had is the voltage sensing fail and tie the batteries together. It didn't have a bad outcome, but could have...

 

That being said, our solar charger has multiple isolated outputs. I am not sure what most have however.

[Island Time 1,239]

Should be no voltage drop across a vsr. I'd expect a terminal problem on a cable, or other poor connection. Take them off, cleanup, inspect, replace terminals or cable if required.