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 ?




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.

Some older phone (like all Ericssons starting from the T28, like the pictured T39) tended to use high quality spring-loaded pogo pins instead (like those that the Jolla 1 uses for extensions, or like the Fairphone2 uses for bus connection between its modules),
and used 2 of them for battery terminals (this increases the contact area, and makes also the connection more secure).
In the photo's case, despite a decade in total of abuse, the pogo ping have held for the whole lifetime of the device (actually, as you can see, the battery backcover retension gave up first).

Another mechanism that avoids damage to the smartphone is the most commonly used with Laptop battery (I've also seen it on my HP Pre3) :
the device has no moving parts. Instead it only has solid straight metal bars. The moving parts are inside the battery : instead of flat contacts, it has clamps that catch the metal bars.

This moves breakable elements away from the device, but just transfers the problem to the battery making it a bit more expensive to produce.