To anyone still looking for replacement batteries you can find a 900mAh sanyo replacement with the current sanyo part number of HF-E5U prismatic battery. I checked and double checked the dimensions and they work. If you follow Toad211's instructions you should be good. However now that I have found the battery with the proper dimensions it's been difficult finding someone who has stock. Apparently Sanyo will only accept orders in the many thousands from their distributors for this battery. So good luck. I'm checking with Dantona currently but they haven't gotten back to me. The GP8M is a very close match as well but I haven't actually gotten my hands on one to see if the dimensions will work. You can get those in small quantities from battery connection at 800-817-0526