I decided to take a look to see if the battery on the PalmPilot m515 could be replaced, and I've found that a replacement (?) battery does exist:
http://www.tangshop.com/palm-m500-m505-m515-battery.html
My only hesitation is knowing how safe it is to replace the battery without losing data or programs.
Will I lose any data or programs by replacing the battery? :huh: