You may be right but since this is the BIOS showing this message that's grim news. Repair will exceed replacement costs so let's try the usual before we write it off.

1. Install the BIOS version that the machine came with.
2. I bet you pulled the battery out and cleaned the contacts. But just so I don't forget to add this item I put it in the post.
3. The batteries are ONE YEAR devices. Proof is the 300 Cycle Rating.
4. In this forum there is a sticky or top post with a note about battery detection in Windows. I re-read your post and maybe it was in Windows? Can't tell.

Hope this gives you a few ideas.