Ok so you're saying I don't really need a PM4 which is approx. ~$25.00 more than the same ampherage PM3?
Perhaps your correct if a battery or battery bank is going to be near it's normal voltage most of it's life and the charger in float or normal mode most of the time.
Progressive Dynamic 9200 series also has a boost mode and doesn't require a battery to be connected for clean DC as it's well regulated.
I suspect the Powermax is similar, works as a well regulated DC PSU without a battery?
PD9200 series
14.4 boost mode
13.6 normal mode
13.2 storage mode
Boost mode rapidly brings up batteries up to 90 percent of a full charge.
Has variable speed cooling fan and other features.
One thing that lowers the life expectancy of a battery is using them at 50 percent charge and less. I think the boost mode may help to extend the life of a battery. It's not quite the same as battery chargers with a desulfation mode, however a boost mode stage may help to prevent sulfation.
RV batteries are fairly cheap compared to solar banks. e.g.
Crown 430 AH 12VDC 5,160 Wh (2) Battery Bank Price: $772.00
Actual deep cycle batteries may require a charger that's better than your average RV charger / converter.
