MinnKota MK-1-DC Single Bank DC Alternator Charger
The MinnKota on-board chargers feature waterproof construction and corrosion-resistant design, a low profile enclosure and turn off when the engine is not in use.  The alternator charger is designed to re-charge trolling motor batteries when the main engine is running.  This means that you can charge-on-the-fly.  Which gives you additional trolling juice when you need it.  This charger is for use with flooded/wet cell, maintenance free or starved electrolyte batteries only.