Would be nice to know what brand that was.

Espar.

Mine
draws 17A while starting (maybe a minute) and 5-7A while running.

that is one hell of a lot of amps overnight. Even a much greater bunch of amps
if you don't move the next day.

btw, you might wish to actually measure just how many amps your system *really*
burns. That brand new system on the boat would run out the about 50 to 60 amp
capacity of the brand new Group 25 in less than about 5 hours. (note a Grp 27
rated in about 105 amps, gives up about half that before it is effectively
dead. That is the way battery ratings work.)