I have an Asus computer and I use it frequently. For the past few months I've been using it while it has been charging. Although, for the past week, when I unplug the charger it will randomly shut down a few minutes afterwards. Sometimes when I unplug the charger it will immediately turn off as well. But more frequently, when I unplug the charger, it will take a few minutes before it shuts down on it's own. Is this because I have been using it while I charge my computer? Or is this not a good battery?