the screws on the battery? do the look stripped? I assume you used the proper size philips. sometimes if its not 100% stripped you can manage to wedge a flathead in there (keep pressure so it doesn't strip more), or if you have the right pliers you can get lucky. if the screwdriver if the right size, and none of the tricks work, you may need to try a screw extractor.
[product|IF145-118]
In the future if the screws are stripping, apply a bit more downward pressure, and there is slipping, don't try unscrewing more until you can figure out why. if its the screwdriver, and you don't want to wait, I love the masterforce micro screwdrivers menards carries, the price is good too.
A good micro shot of the screws could help us out a bit more too.
Sorry I can't help more :(