I fully charge my laptop's battery and when I hover over the battery symbol on the toolbar it tells me it is 100%. Then shortly afterwards, about 1 minute later, it tells me there is 4 minutes of battery power left! If I do not charge it quick enough it turns off. It is a brand new laptop which I got 16 months ago and up until 2 months ago the battery was perfectly normal. It is used almost every day for 1-2 hours and is charged regularly when needed.
It sounds as if the battery is either shot or it needs to be fully discharged. Try letting the laptop completely die, i.e. let the battery discharge all the way and then charge it. If it continues to do the same thing, chances are that the battery is shot.