First off, you'll never have a problem where your computer will no longer turn on. As long as you have your charger you can plug you computer into the wall and take out the battery and the laptop will work just fine. That being said I think your problem has to do with what ChosenOne said, once devices such as cell phones or laptops are at full charge it is best to unplug them and let them come close to dieing before recharging. They should not be plugged in at all times it kills the battery. If I were you I'd let the laptop die. Then plug in and my charger and let it full charge before using it again. If at the very least you will see how much battery time you have on your charger.