This is really cool project, but please be careful if you're considering building or purchasing these for emergency or accessibility-related reasons.
The phone's build-it-yourself kit instructions[0] mention that the battery and signal strength indicators aren't yet functional.
"Currently, battery and signal strength metering is not working. I hope to have this fixeed in firmware soon, but this further complicates the above quirk. If you have a voltmeter, it's easy to probe battery voltage without opening the case vai the ICSP header on the back"
From previous discussion[1] it sounds like the battery life is approximately 24h.
Not to be a downer but sometimes it concerns me when we celebrate things which people might consider useful for critical infrastructure when they're not ready.