Matt,
I successfully ran my IV-P pump and gear for many months (before the battery
was in place) with a 15 amp 6-12-24 volt battery charger.  It doesn't run
any better with the battery in place than before, as far as I can tell.  The
charger is probably under rated.
The max load current is most likely at inrush and just before cutout as the
accumulator takes up it's max charge.
Walter Dodson  IV-P 85%