In case you are looking for a replacement battery for the PRS-300, I used one meant for PRS-505 (LIS1382-J), and it works fine.
I purchased it on Batteryship.com (
http://www.batteryship.com/htmlos/ht...Reader+PRS-505). The battery is a little thicker than the OEM battery so I had to remove the metal tray that houses the battery to accomodate it.