The Battery Tender Solar Charger 021-1177 is a solar-powered battery charger designed to keep 12-volt lead-acid batteries fully charged and maintained. It uses a built-in solar panel to collect energy from the sun and convert it into electricity to charge the battery. This charger is ideal for use on vehicles that are not in regular use, such as motorcycles, ATVs, boats, and RVs. It features a 3-step charging process that ensures the battery is charged safely and efficiently. The charger also has a built-in smart microcontroller that monitors the charging process and adjusts the charge rate accordingly. This helps to prevent overcharging and prolong the life of the battery. The Battery Tender Solar Charger 021-1177 is compact and easy to install, making it a convenient and eco-friendly solution for maintaining your batteries.