The Battery Tender Solar Charger 021-1171 is a solar-powered battery charger designed to maintain the charge of 12-volt lead-acid batteries. It features a built-in solar panel that collects and converts sunlight into electricity to charge the battery. The charger also has a microcontroller that monitors the battery's voltage and adjusts the charging rate accordingly to prevent overcharging. It is compact and weatherproof, making it suitable for outdoor use. The Battery Tender Solar Charger 021-1171 is an eco-friendly and efficient solution for keeping your battery charged and ready to use.