A small suggestion for the battery connection for your smartphone project. If possible could you consider a similar assembly, with double high quality pogo pins on + and - battery terminals ? http://www.sympato.ch/~dryak/files/t39-battery-pogo.jpg The prongs that smartphones such as the Jolla 1, Fairphone2, etc. use tend to bend, break, or (in my phone's case) break their springs quite easily. This leads to spurious reboots whenever a bad contact causes a transient power loss.