My battery was shot and would no longer hold a charge. I found a replacement 500mAh lithium polymer battery on eBay that is very close to the physical dimensions of the original 430 mAh Li-Po battery. You just have to shave the little plastic ridges away in the area where the battery sits with a sharp knife for a perfect fit. In order to connect it to the internal electronics of your ClamCase, clip off the battery connector and red/black wires about half way on your original battery. Then solder this connector and wire assembly onto the wires of the new battery. It works great, and now my ClamCase has come back to life once again.
The replacment battery can be found here: https://www.ebay.com/itm/3-7V-500mAh-392263-Lithium-Polymer-LiPo-Rechargeable-Battery-USA-STOCK/174275407620