If it's an old laptop or one that gets heavy use with it often plugged in, this simply means your battery is knackered. Most people don't really know how to look after a laptop and just have it plugged into the mains all the time. This quickly knackers up your battery as the best way to maintain it would be to charge it and run it right down to 3-4% and then charge again - hardly ever having it plugged into the mains.
If your laptop is under a year old, and does not get plugged into the mains during most uses then I would suggest getting a new battery on warranty but be prepared to hear the same as what I've told you.