A battery charger is a device that replenishes the energy stored in rechargeable batteries. It works by supplying electrical current to the battery, allowing it to regain its charge. Common types of battery chargers include those for lithium-ion batteries, often found in smartphones and laptops, and NiMH chargers used for household devices like remote controls. Battery chargers come in various forms, including wall chargers, car chargers, and portable power banks. Some chargers are designed for specific battery types, while others can charge multiple types. Many modern chargers also feature smart technology to prevent overcharging and extend battery life.