Unlike dual power, which requires two separate battery cartridges, the Twin Power flashlight operates seamlessly with a S cartridge. The cartridge holds a built-in 10850 rechargeable battery for primary power, and 4AAA alkaline batteries for backup. With this innovative design, you'll never face the dilemma of drained power. Simply toggle between alkaline and rechargeable battery sources with the touch of a button, ensuring uninterrupted illumination whenever you need it.