Why does my Samsung Galaxy Fame keep randomly switching off?

[AC Question]

My Samsung Galaxy Fame was bought in December 2013 and since about February 2015 it keeps switching right off when I haven't manually switched it off. It does it even when I don't have low battery and it is really annoying as I have to go through the whole rigmarole of waiting for it to switch back on. It happens when I'm on the phone most of the time, if that helps. Thanks.

 

[Rukbat]

After it happens and you turn the phone on again, look in the battery statistics (in Settings). Tap on the graph to get to the second page. Lopok for a sudden drop to 0 (it's called "falling off the cliff"). If you see that, the battery is throwing a dendrite (see Lithium Battery Dendrite links) and has to be replaced.