Before you start thinking about buying a new battery, check out your old one first. I nearly threw mine away, but read some posts on line which prompted me to strip mine down.
What I found was that there is a tag at the end of the inset black lead which comes from the mini circuit board.
This goes through the plastic plate and makes a connection on the end of the run of "sausage like" battery cells. This tag had snapped because it is so flimsy.
This tag can be soldered with care or run a small piece of copper wire through the plate and solder to both halves of the tag.
Now my battery works as good as new.
XaiviaX
September 2012