Earlier quoted context omitted.
I actually got stranded once for some hours because of the mileage indicator! Was driving back from a campsite that I turned out to not have charging compatibility with, but thought I had plenty of margin to get to the nearest charger. As I drove through the mountains however, I began noticing that a.) my battery was depleting much faster than expected and b.) I wasn’t seeing any houses and very few motorists. I watc…
> it was pretty hot and we had no water. Another take-home lesson: if you're driving out of range of civilization, carry water along with your first aid supplies.
If you're in an emergency and your phone says you have no signal, call 911 anyway. It'll attempt to reach any network in range that the phone is compatible with, not just the network you're subscribed to. Some phones nowadays will show "Emergency calls only" when this is the case, but it doesn't appear to be 100% consistent, so again, call anyway.
Also turn on battery saver and when you're not actively trying to call, keep the phone in airplane mode. If you don't it'll repeatedly try to reach a tower which will drain your battery quickly. Don't power it off unless you don't plan to use it for the rest of the day, because booting up uses a lot of energy.