Most people (myself included) have a tendancy to run their laptops on the mains most of the time. This will kill the battery sadly.
I bought mine secondhand, and the battery was already pretty much useless, so am just stuck with mains, but we make a point of using Hannah's one on the battery as much as possible, as we bought hers new.
You may have a fault with the laptop, but I suspect it's just that the battery is now an ex-battery (he says, in a Monty Python style!)