This is a waterproof onboard Charger/Maintainer that can charge/maintain up to 3 batteries at once! Just plug your extension cord into this unit after your fishing trip is over and leave it alone, if you want to fish again tomorrow or 6 months from now, this charger will ensure your batteries are ready when you are. 12-36 volt - 10 amps per bank - 30 amps total - 4.5"Hx8"Wx11.25"L - 15.5LBS.