Laptop keeps restarting unexpectedly, but only when plugged in.

It's getting so frequent that it is impossible for me to work properly, when the battery life is not high enough. Mostly I can get around this, but on long days it's not possible.Laptop crashes ~ every 20-30 minutes. The only information on the Windows Reliability Monitor is the following: ProblemWindows not properly shut downDescriptionThe previous system shutdown at "time" on "date" was unexpected.The time of the unexpected shutdown is always around 10 minutes before the actual restart occurs. So say, the laptop restarted on 9:00 AM then the Description would say: The previous system shutdow