$SportDOG SAC54-13735 Rechargeable Receiver Battery Kit for SD-425 Series & 825. The SportDOG Brand® SD-425 and SD-825 Series Receiver Battery Kit includes a rechargeable battery. Efficient by design, this battery kit powers a transmitter so you can uninterruptedly train your dog into being the best behaved dog on the block.
The complete sets I got were great but half the kits I got were missing part of the kit so I would suggest buying a gun dog supply instead at least you'll get a complete kit and they're about the same price.