Looking for a battery issue

[jaisanthosh44]

I am having a Dell laptop. But after a 2 to 3 hours of charging its laptop and it's battery is full. But then after using a laptop for an half an hour, my battery power is going to 50 %
So please tell in what is the problem in my laptop

 

[1shado1]

How old is your battery? Sounds like it's shot.