What is the mathematical formula to calculate the voltage of a (typical) LiPo battery as a function of it's charge, current flowing and external temperature?
Whilst I cannot provide you directly with a "generic" forumula that will solve your answer I'd suggest you perform an experiment like the one completed in this youtube video. You'll need to insulate the battery in a fixed environment at a temperature you are keen to analyse.
With the raw data you will be able to derive an equation. I highly suspect that you'll find huge variances based on the number of charges the LIPO has gone through and I suspect your results will vary based on LIPO age as well.