So I built one of Charles Hallard’s PCB’s in April of 2018, that is 50 weeks ago. I received a batch of 3.3v LiFePO4 batteries, 18650 size and I clipped one into the battery holder of the PCB, the voltage was 3.3v.
This has woken from deep sleep 96 times per day to report environmental data from a shelf in my kitchen and this is how it looks today:
Operating from a LiFePO4 battery without any regulation is perfect IMO, perhaps I could have topped this cell off to 3.6 or 3.7v which I am reliably advised will not fuse the Arduino or the RFM95 but I didn’t and it still works very well.
If you are considering LiFePO4 then look carefully for a charger that can sympathetically charge these cells (they are different to LiPo !). Our in-house guru @BoRRoZ is testing a super good value bench power supply which would do the job nicely and lots more…
HTH?
G