OK look at the charging end of the battery, and in the middle you will see
a metal bit, not a pin exactly, but its the centre pole (for want of a better word)
If you have some thin nosed pliers, or even a straightened our paper clip, you
can give that centre pin (pole) a bit of a wiggle (of course please be gentle, you dont
want to end up with the centre pin in your pliers and not attached to the battery anymore!)
sometimes this will raise it just a mm or 2 to make it connect with the charger centre pin....
if thats what the problem is to start of course!
If that isnt the problem, then it wont charge.
The thing is sometimes, attys that we use can knock this centre pin in the battery
down by just a millimetre and then it wont charge....