The only time I've been running out of battery on a phone was when I picked up an unknown smartphone lying in the snow years ago. It had very little power left. I guess what happened in this chapter indicates the level of the MC's nervoussness when he didn't even check the battery status.
@Abedeus
That's only if battery is not shit - those can suddenly turn off even at 30%. Albeit, he wouldn't have seen low battery indicator in that case.