Originally Posted by
noglider
A few months ago, I got a reconditioned iphone 12. It's in such good condition that I can't tell it's been used, and even the battery is strong. Anyway, it gives me the impression that the GPS receiver is not a power hog. I haven't done any measurements, though.
I am familiar with Android phones, not Apple. I have an app on my Android phone called AccuBattery Pro. It calculates all kinds of statistics on my battery usage. I have not tried to figure out what would happen if I left the phone on but no apps running and airplane mode for a day, and then repeat with GPS on and a GPS navigation app on. But if I was interested in trying to figure out my power needs, I would probably do something like that.
Or skip the power usage app, just let phone sit turned on, airplane mode and all apps off for a day and look at percent change in battery level. Repeat for a day with GPS and navigation app on for a day and then check percent battery usage change. You lose a bit of precision looking only at difference in percent battery usage, but that probably is more than enough for making estimates for bike touring needs. If you are relying on dynohub for your power needs, you get a lot of variation from day to day riding depending on how hilly the terrain is, you can't really say that you expect to get X number of watt hours of power per day of charging by dynohub. That is why I want a pass through cache battery that has a capacity of several days of usage.
My GPS (a Garmin 64 general recreation GPS, not a cycling specific one) uses roughly a half watt when on and backlight off. I figured this out from letting it sit turned on with a set of freshly charged NiMH AA rechargeable batteries until it shut off. The track it maintained as it sat there gave me the time of operation until it auto shut off. With backlight on full, the same kind of test told me that I can cut that run time in half. With screen off 99 percent of the time appeared to have almost no difference than screen on and backlight off, which surprised me. Apparently the screen on with backlight turned off uses almost no power difference than with screen off. Thus, I now just leave the screen on full time, but I am obsessive about keeping my backlight at only the minimum that I need which is usually none. This GPS has no connectivity for wheel sensors, HRM sensors, no wifi or bluetooth, simply just doing the GPS thing without devoting any power to other uses.