[Michael]

We use the previous model of this in our coach.

https://www.marinco.com/en/p/2720A/Guest-On-Board-Btery-Charger-20A

We are very happy with it. There are other options as you shall see.

I don’t use it often, only when the chassis batteries are low, which is rarely. Our coach just sat from December 2nd to Wednesday of last week (over four months) in an unheated building in NE Wisconsin; mostly below 32*F, some sub-zero. When I flipped the 12 and 24 volt chassis battery master cutoffs to ON, there was plenty of power in the batteries to start the big Detroit.

I have the charger for (1) when I screw up and leave something on (like lights), (2) if the batteries start to get old and weak, or (3) something happens to the batteries. If your batteries seem to discharge by themselves quickly, you might have something wired to the “hot all the time bus” incorrectly or your batteries are on their last legs.