Originally Posted by
ttsoldier put phone in refrigerator. LOL!
When the phone displays an empty battery sign while updating it's because it overheated, not because the battery is empty. So putting the phone into a fridge is actually a good idea :D It happened to me yesterday and then I had to rollback, because nothing else seemed to help. If the phone were in the refrigerator it might have worked. I am going to try it today, just for the fun of it.
ETA: I hate to bring this up, but I was updating my brother's Note 4 to Lollipop and it went very quickly and without any glitch or overheating while updating WP is always one big PITA.