9 times out of 10 this is down to using the wrong lead or the wrong plug.
Always use the lead provided and a plug that will let a slow trickle charge in Usually this is a 5v 1amp plug.
If this is what you have been doing let the battery run down low and then plug the USB into your computer USB socket. This is often a very slow charge of 300mah or less, batteries like this as it gives it plenty of time to soak up all of that good energy.
Batteries that have been charged incorrectly for a while will need reconditioning with a few slow charges to get them back to a better performance
