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 adapter, 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 setup will do in a pinch,...
M/F Connect the Mini-B USB cable to the USB-to-AC adapter.
M/F Plug the small end of 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.
M/F Connect the USB-to-AC adapter to a wall outlet. The Nintendo DS power indicator light will turn orange when charging.