battery ups and downs after using the run+ app

After running with the run+ app, the battery level often ends up in the red zone. But, after the run is over, the battery gradually comes back to a higher level. In the attached pictures, it shows maybe 10% at the end of my run, and 1 hour later (and probably even before that), without any charge, it's back to the green zone, around 35-40%. So far I had the case only twice where the watch goes flat during the run, so I'm not too concerned. Basically, it works, I'm just wondering if there's something to be tweaked here.

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If you suspect there's something specific to run+ maybe you could try using the run app for some runs to verify if that's the case. If so we could look at the code specific to run+.

I don't see why they should behave very differently with regards to power load. But if they do that's interesting.

As discussed in various places, the battery indication will vary with power load. So particularly if you use both GPS and HRM (and especially if the screen is kept on) it will dip compared with lighter loads.

Also, if the watch gets significantly colder (if it's exposed to cold weather while exercising maybe) I think that could affect the indication as well. But your body heat should probably even this out.

As @Ganblejs says really...

When there's a high power draw (eg GPS) the voltage from the battery drops because of the internal resistance, and so it shows a lower capacity. In some sense it's true though - you could run the watch at 0% for a while normally, but if you run the GPS when it's at say 5% it might cause the watch to turn off.

The temperature can have an effect too, and I guess maybe there is a possibility of adjusting the reported voltage by some fudge factor based on temperature - but it's all really handwavey and I imagine probably depends on the age and batch number of your battery. I think there's a significant chance of overcompensating and making the battery read too high on some watches - so I wonder if it's just better to leave it as-is.

However nothing at all stops you making a new 'compensated battery' widget (or even boot code that replaces the E.getBattery function with a compensated one). You could even check the power status of the main users (GPS + screen) and adjust based on those too.

edit: potentially you could make an app that deliberately turns the GPS and LCD on and measures the difference in battery voltage when you install it, and then applies those tweaks i the future.