I just replaced the battery in mine. Soldering was the hardest part but only because the whole circuit board acts like a giant heat-sink, which made it almost impossible to properly de-solder. I couldn't get my iron's temp dialed in right and was running out of time/impatient. I cut the battery wires as close to the PCB as possible to get the battery out of the way and free up a hand for temp adjustment. In my case it seemed like I was going to burn the PCB before the solder mounds could flow. I de-soldered what little I could and simply tacked the new battery leads onto the existing mounds. Once both were in place I adjusted the heat and re-touched each mound with a little more solder, until it looked like a good joint but it's definitely not perfect. Some of the charging terminals on mine had holes which caused charging to fail, so I added some solder. So far so good, seems like it's almost done recharging.