A bow thruster is a high-load, short duration device. House batteries are not designed for this service
. Engine starting batteries are. (Same for your windlass
.) If you need to add another starting battery to your circuit, that's fine, but I would not recommend using your house batteries for a thruster because it will wear them out prematurely. (Experience speaking here...$$$!) If you have to add a separate battery, make it a high capacity starting battery and put it in the bow. Wire the windlass
to this battery too, and then your house and engine starting battery banks will last longer and be protected from excess wear and damage. Also, get a long set of jumpers and you can use the windlass/thruster battery as a backup to start your engine if you have to. Check your charger
; some of them can handle three separate circuits when you're plugged in to the beach.