Philips Norelco BG2040 BodyGroom 7100 Battery
+1 to Michael Hendricks. I ended up putting mine in my toaster oven (which worked splendidly), and I did have to use an x-acto knife to get it started. After that, it was possible to continue using the picks, but DON’T EXPECT TO BE ABLE TO REUSE THE SAME DISPLAY. New displays are $35 on ebay. Just get a new one before you start the work or you’ll almost certainly be without a phone for a week.
+1. Don’t bother trying to save the screen. Just save yourself the stress and buy a new screen on ebay for $35 before you begin. I have never botched a repair and I still managed to break my display on this. Yes, I was super careful, it took me like 45 minutes to finally get the display loose, and when I put it all back together, the display was totally dead.
Note: the pictures make it look like it's the glass the comes loose from the body. In fact, it's the metal shell the comes off, while all of the electronics are attached to the face. To get it started, you have to dig your spudger in between the metal shell and the little plastic rim that goes around the glass. I found it easiest to start in the middle, below the volume buttons.
Unfortunately, it would be hard to find a cell battery this small. The original battery is 2" x 1 1/8" x 1/8". My samsung S3 battery is 2 1/2" x 2" x 3/16", so is far from fitting. If you were ok with shaving the molded battery holder down, you could probably fit one that's 2" x 1 1/2" x 1/4" or so (the thickness tolerance is hard to tell), but it would be a lot of work. I think I might just buy a speaker that has good battery reputation (i.e., NOT JBL).