Sunsei 25006 SE-500 7.5-Watt 15-Volt Solar Panel Battery Charger / Maintainer 7.5-Watt (500mA, 15-Volt)solar charger, perfect for medium sized boats, R-Volts, trucks and tractors Protects against natural battery discharge and electronic drain Touch-action indicator Engineered to maintain your 12-Volt deep cycle battery Perfect for back-up power in RVs, boats or off-grid applications