If you've lost or damaged your Nintendo DS battery charger, you can make one using a Mini-B USB cable, the kind used by most digital cameras, and a USB-to-AC adaptor, the kind used to charge USB devices using a wall outlet. The port on the back of a Nintendo DS is about the same size and shape as a Mini-B USB port so this set-up will do in a pinch, but prolonged usage is not recommended.
Connect the Mini-B USB cable to the USB-to-AC adaptor.
Plug the small end of the Mini-B USB cable into the charger port on your DS. Because of the shape of the USB cable, you'll need to push a little harder than you would with your normal DS charger so use a bit of caution when doing this.
Connect the USB-to-AC adaptor to a wall outlet. The Nintendo DS power indicator light will turn orange when charging.
You can use a Motorola mobile phone charger to charge your DS, too; the plug is the same shape as the small end of a Mini-B USB cable.