Eric, if the battery you need is 4.2 volts, you might look at the older style camera or flash batteries. I got a 4.5 volt flash battery off the shelf at Walmart years ago to put in a Hoffman transistor radio. It wasn't quite fat enough to stay in place, so I wrapped electric tape around the middle of it so it wouldn't bounce around inside the battery compartment. Worked like a charm.
Don't recall the battery number, and I am on the ship right now, so I cant go digging around to find out what I did. However, here is a photo of what I did...
http://www.videokarma.org/showpost.p...07&postcount=6