How do you mean? Sorry if I'm a little slow. 
I tried testing in just below 0°C and now I just bothered to take notes on method 2 and 3 since 1 was too far off.
Powering using USB:
4.47V (measured using my meter)
4.45V (method 2) diff 0.4%
4.39V (method 3) diff 1.8%
Powering usning 3S:
11.55V (measured using my meter)
11.56V (method 2) diff 0.1%
11.54V (method 3) diff 0.1%
Now if it gets even colder I will try again but for now I pretty happy with method 2, it seems to be very consistent with my meter which was what I strived for in the start.