A battery charger is a device used to replenish the energy stored in rechargeable batteries. It works by supplying electrical current to the battery, allowing it to regain its charge. Battery chargers come in various types, including wall chargers, solar chargers, and car chargers, each designed for specific battery types and applications. Most battery chargers are equipped with indicators to show the charging status, such as LED lights that signal when the battery is fully charged. Proper use of a battery charger can extend the lifespan of batteries, making it an essential tool for devices like smartphones, laptops, and electric vehicles.