Screen froze, possibly battery?

Just a few hours after I made a thread asking how to keep my Nexus 9 working for as long as possible I ran into trouvle. I was using my Nexus 9, surfing on Chrome in landscape mode while it charged ( battery was on the low side) suddenly the screen froze with some greyish horizontal small line segments and it would not turn of. After I held the power button for quite a bit longer than I'd have to normally it powered off, but not on again, not even that little vibration, so I let it charge for a while, then that little empty battery sign appeared but it would not turn on, after a few more minutes it had changed to the charging animation and turned on, and it turns out the battery was at 3%!
Now, it does seem like it just ran out of battery even though it was charging, but if it was just that why did it freeze so hard and why did I not get any low battery warnings?
Thanks!