I’m planning on using a smart-phone (5V) backup battery to power my photon based project. I would like to be able to detect from the onboard voltage regulator of the photon that the battery is getting low so I can signal the user to replace the battery. Is this possible?
Alternately, I believe I could use something like shown in the image below where I connect the incoming line between the two 3.3KOhm resisters to an analog port of the photon. Is this the recommended option?