New On-board Dc Alternator Charger minn Kota 1821033 Model MK-3-DC Banks 3 Amps per Bank 10 Total Amps 30 : Alternator charging design uses current from boat s alternator to re-charge trolling batteries when main engine is running. Charge-on-the-fly circuitry puts additional juice back in your trolling batteries on runs between fishing spots - turns off when the engine stops.