Won't run on battery

My mother has the Santa Rosa model of the Macbook Core 2 Duo that she received as a work machine. She told me that it won't stay on unless plugged in. I had her check to see if it said her battery needed to be serviced/replaced, it didn't. It only says that the battery is not charging. Does this mean she needs a new battery or that it's something more internal?

It's hard to be more descriptive than that since I haven't actually seen it..but any suggestions would be greatly appreciated. Thanks!