The Battery Tender Solar Charger 021-1173 is a compact and efficient solar panel designed to charge and maintain 12-volt lead-acid batteries. It features a built-in smart charging controller that ensures maximum charging efficiency and protects against overcharging. The solar panel has a durable and weather-resistant design, making it suitable for outdoor use. It also comes with a built-in temperature compensation feature to adjust the charging voltage according to the ambient temperature. This solar charger is ideal for maintaining the charge of batteries in vehicles, boats, RVs, and other outdoor equipment.