Thanks, Base. The 'power' setting is supposedly the default for the USB port, according to the manual. I got charging actually working today, using an old USB A to USB mini cable, and a separate USB A to USB C adapter. Unfortunately the adapter does not fit my phone very well. I ordered another simple (I hope) USB mini to USB C power cable (no OTG, no special high speed data transfer specs), maybe that will work. Worst case I will machine this adapter down a little bit. So, there is hope.
The Jepster app I was using to record the power sensor data (via bluetooth only, no Ant+ from the bike) unfortunately lost the GPS data all the time after a few minutes, and when I updated to the latest version the app crashes immediately when I try to start a recording, or try to open an old recording ('activity') for analysis.
Luckily, it seems the Wahoo android app works: it records GPS and power (and heart rate and cadence and speed) reliably, and uploading into Garmin Connect is made easier (compared to Jepster) by an automatic emailing feature for the .fit file. The app also has a pretty nice data and data + map display, similar to Jepster.
So, I am getting closer to a working setup.
