Monitoring battery status of other phones, on 1 phone


I have an old S4 that I want to keep in my car at all times, so that I can always locate the car through it.

What bothers me is how to keep it from running out of battery without me knowing.

So I wondered if there was an app that would alert me on my other phone (S7), when the S4 in the car is low on battery.

I've managed to google up one app that seemed to have this functionality (named Potential Beta), however, the project seems to be abandoned and the app no longer works.

Does anyone know of any other apps that do this?