It pays to have one or more extra cell phone battery packs for emergencies. Staples has had them on sale for as low as $5.00 U.S. They go up to $80.00 or so. There are many brands available.
In the event of
an emergency were there may be indefinite loss of power.
(1) forbid the children from using cells for games.
(2) lower screen brightness in "settings".
(3) shut the phone down completely when not in use.
Cell towers may be jammed during the daytime and you will have a better chance of making a call
during night hours.