The battery can be replaced, but getting the case open (without damaging it) requires the right tools. Something similar to these;
http://www.dealextreme.com/details.dx/sku.3006 (those are not the ones I used and might not be strong enough. I don't recall where I got mine.) There are screws under the rubber "feet" on the back. Remove those first (stick a needle into them from the side and pry up gently). Once open, the battery is rather simple to remove/replace.
Opening it will probably void the warranty though. I would contact Ectaco first, especially if it is still under warranty.