Another alternative is to put a outdoor light timer on the circuit and only charge for at set amount of time a day. I did this after boiling my batteries once. I set it to charge for an hr. a day and it kept the batteries right up. That was in -10 and colder weather.
My coach has a solar charger that I now have working and it trickle charges both sets of batteries. I just turn off the disconnect switches and the solar maintains both sets.
If you do connect both sets together use good connectors as suggested above.
Dennis & Marcie & Hook The Jack Russell, 2001 HR Imperial 38wds 350 Cummins, 07 Chevy Trailblazer/Blue Ox/Ready Brake, 04 Dodge 3500 Cummins,