Well, hate to slow ya down, but dont expect to just open the hood and swap out the battery.
If it's anything like all the other proprietary stuff Alesis dumped on the market, the battery is soldered in.....and you wont be able to buy a new one at Radio Shack, you'll have to search for the exact match online. Do a search, there is another thread specifically about finding batteries for Alesis gear. Do a search on HR16 or SR16 (HR-16, SR-16, similar syntax) and you should find it right away.