Great idea... I saw this and thought I’d pass it on… If you are ever lost while hiking, get stranded with a broken down car, etc... and you notice your cell phone battery is dying, here is a tip that very well may save your life. Change the voicemail on your phone to a message that gives your approximate location, the time, the date, your situation (lost, out of gas, car broken down, injured, etc...) and any special instructions such as you are staying with the car, you are walking toward a town, etc.... The best part of this is that even if your cell phone dies or stops working, voicemail still works, so anyone calling your phone looking for you will hear the message and know where to find you or where to send help.
For $20-60 you can also carry one of these with you, you can fully charge from 0-100% most modern cell phones 5-6 times. That's about 1-2 weeks of battery life depending on the phone and how much you use it. https://www.amazon.com/Anker-PowerCore-Technology-High-Capacity-Compatible/dp/B07S829LBX/ For $12 or so you can get a car charger - https://www.amazon.com/Anker-Charger-PowerDrive-Adapter-iPhone/dp/B07PGT7LSR/ We go hiking out in the mounstains often, 6-8 mile hikes regularly. One tip is to charge your phone on the drive out there so you start the hike with 100% charge. My phone (at about 1.5 years old with at least 100 apps) stays charged about 30-36 hours usually. If you really were going on a true backcountry hike for multiple days, you can also get a small solar charger. With that, you could pretty much keep your phone alive forever for about $50 https://www.amazon.com/30000mAh-CONXWAN-Foldable-Charging-Flashlight/dp/B08VW6CBTZ/
