Laptop problems when unplugged from the mains?

[missmetzner]

So when my laptop is unplugged from the mains it starts playing up, after use for a couple of minutes it just crashes the screen, then the mouse, then either comes up with the blue screen of death or a black screen which asks me to insert the boot drive or something (?) then won't turn back on until i plug it into the mains charger, where it will work fine. The laptop is a Dell Inspiron 15 and is just over a year old, the battery life is fine and usually lasts for 4/5 hours, please help!