RE: Trickle chargers or Battery Maintainers
The small (5 amp or less) battery maintainers or trickle chargers are meant
to keep a battery topped off when NOT inuse, not load on the battery.  Like
in the garage for the winter.  They will not charge a bettery that is down
or has a working load on it.  I've tried to use one to maintain an aux
battery (working battery) and got zero increase in the charge on the battery
after a couple of hours.  So if you have your rig parked for extended
periods of time and also have access to shore power, fine.  But for a rig in
use, with loads on the aux battery, go with something larger.