Cameron that is lot of power use.
Yes, it is a high figure that has been consistent across at least four different iPhones I have owned. GAIA claims that even though their sample rate is high, power consumption would not change if they dialed it back to one or two minute samples, probably because the GPS is constantly in seek-mode regardless of sample rate. Could it be that you are only consulting CalTopo but not doing continuous tracking? Off-trail, I have continuous tracking on and I also wake up the iPhone constantly to check my position. I don’t use it to tell me where to go but I certainly do constant reality-checks.
However my attribution of power use to GAIA may be incorrect and I should do a careful test isolating GAIA use only. I take a ton of photos which could be another prime power culprit. (I also never realized until this last summer how much the photo-taking slows me down. Walking with someone else, I kept falling far behind! The photo-taking probably adds an hour to my hiking time every day, but for me it is an essential way that I engage in the landscape and what I am doing.)
Returning to your calculation, Alex, I walk 10-12 hour days. So let’s say that amounts to at least 24% drain on your 5,000 mAh battery = 1,200 mAh. The typical fresh best-case battery efficiency is around 70%. So that one day of Caltopo use costs 1,714 mAh in battery. That would mean that a typical 10,000. mAh Anker battery would only give you 6 extra days of GAIA use, and it weighs over 5 oz.