@jremington
I've already seen how reading the voltage of the battery would work online, given for example right here:
and here
http://www.instructables.com/id/Arduino-Battery-Voltage-Indicator/ (just without the LCD, the battery being 3.7-4.2 V connected to a TP4056)
Anyway, here is my diagram named PwrMngmntMdl.png
I don't know where to attach the Low Battery Indicator circuit. I just need the low battery LED indicator and voltage indicator from the sources I stated above. 
