Saving problem

Hi,
I just bought a boxed copy of VB Wario Land (US) off of eBay, and the save feature won’t work. Whenever I turn off the system for more than about half a second, the game erases all data. Does anybody have any idea what’s causing the problem (I think the battery is dead) and whether or not I might be able to fix it myself? Or, should I just return the game? I want to try out the game really badly because everyone says it’s the best game for the system. Thanks!