This has happened at least twice so far. While updating a bunch of apps, my iPhone 6s (iOS 9.3.4) will suddenly shut down as if the battery is drained. If I try to restart it, it will shutdown again after a few seconds. Occasionally I'll see the image of the empty battery in the center of the screen while I'm trying to restart it, yet my battery indicator in the upper corner will read, say 34% (when I do get it restarted for a brief moment). Only plugging in the iPhone stops the repeated shutting down. And again, when I plug it in, the upper corner battery indicator indicates I still have plenty of battery power. Any idea what causes this? Thanks.