My phone regularly runs out of electric power.
I have one of those battery packs now. Have only used it once, my thinking is that I should be doing something more useful instead of reading crap on the phone, but it is the easiest thing to do when time between changing trains is short and one is standing.
The battery is removable, but it is a process, I thought Android was crash-proof, all of the seven, eight or ten times I have removed the battery, it was to reboot the thing because it crashed. Albeit, this is over two or more years.
Why they didn't include an external reset button, accessible by toothpick or pin, I never understand.
I really preferred my TRON mini-brick in many ways. It *never* crashed. Still hasn't.
Off topic, I saw a lady on the train today who had decorated her iPhone with marker pen, I thought 'That's the spirit!' She'd written 'OH MY' with nice balance on the top, and G and D! on either side of the round button in the lower centre.
Applying marker pen to a sillyphone, very stylish IMHO.