Sony Vaio Battery Troubles?

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I have a Sony Vaio, and recently it has been having problems with the battery not being recognized. Sometimes when I turn it on, the computer will say that it does not recognize the battery (which is the original one that came with it when I purchased the laptop about 6 months ago), and that it has to go into hibernation mode while I repair the problem. I let it go into hibernation, then immediately turn it back on (even without doing anything to the battery) and it works just fine. The first few times I removed and reseated the battery, but now I just turn it back on without messing with the battery. Has anyone else had any experience with this happening with their Vaio laptops? Any idea what causes it or how it can be fixed?