I put in a new battery a while back an off brand and it still did not work.
But although this video leaves alot to desire it does talk about why many stop.
http://www.youtube.com/watch?v=3Z-3m4Ljwiw
He does a bad job of showing you where the screws go but if you can get there it seams like a simple fix.
anyway you get to see the insides of it too.
got better answers??
Ron