Rechargeable D batteries are bigger than the commonly used AA and AAA batteries, and are capable of providing more power and a longer lifespan in high-energy devices. Due to their size and capacity, rechargeable D batteries are often used in larger electronic devices that require a lot of energy, such as flashlights, portable radios, boomboxes, and some toys. This makes rechargeable D batteries a practical and convenient choice for these types of devices.