There are a lot of threads on using a old android phone to USB tether to a raspberry pi for internet access. I am trying to tether a RPi to an android phone to allow passing of MQTT messages to my farm irrigation valves (esp8266 based). The idea is for me to be able to go out of town for a week or two at a time and have reliable connectivity to trigger my irrigation system. It is working (Galaxy s4 on Ting wireless, RPi3, Home Assistant), but the phone keeps untethering every few hours. Would Wifi tethering be more reliable? Should I root the phone and change operating systems?
Any help would be appreciated.