most chargers made today that are automatic are multistage. They detect the voltage level, and adjust the amps accordingly. They may charge for 2 hours at 10 amps, then back off to 2 amps when its 75% charged to allow cool down and absorption charging until fully charged. Then they trickle charge as needed to stay topped off. Really worth the $75 investment for a single bank automatic onboard charger. Just mount in out of the way in the boat, and plug it into an extension cord when your done fishing.