My HP laptop battery dies quick?

I bought my HP laptop about 5 months ago, and it says that the HP Laptop Battery life takes about 4 hours or so, but my laptop is dumb. I was charging it and it said fully charged and after 3 mins, it has 91%Laptop Battery. And the brightness is not even bright anymore, its like dark -_- just to save my battery. Anyway is this normal or do I need to replace my battery? Or maybe it is time for me to buy a Apple Laptop Battery.