When lithium-ion rechargeable batteries first hit the market, they were a big deal. They opened a whole new door to portable electronics, because even though the battery could only power it for a few hours, they could be used over and over again.
Unfortunately, this use cycle was not unlimited, and they could only be charged and discharged about 300-500 times. The number of charge cycles has greatly increased since then, mainly due to intelligent charge controllers in the electronics, however, it is still not unlimited.
Chances are, if your laptop is a few years old, the battery has undergone cell oxidation. Cell oxidation is when the battery loses electrons. This is normal, because the battery outputs electrons in order to power the device. The degradation of battery life is caused by the fact that not all of the electrons can be recovered every time the battery is recharged, so, each charge cycle you put the computer through slightly reduces the battery life.
Eventually, once the process gets far enough, the charge controller will notice and send a message to the device. This usually shows up as a notification in the lower right corner on Windows systems. Unfortunately, due to the nature of lithium-ion batteries, there is no way to reverse the process. The battery will need to be replaced.
If this has happened to you, consult the experts at South City Computer to find a reliable replacement battery at a good price.