After many tries to start discharge at a point to get a successful calibration, I created this small script which other people might find useful:

It stops BME, and starts the charge21.sh script.
After that, every 30 seconds - the RSOC is being tested and if it reached 100%, it goes to sleep for another XXX seconds (you can change the value of the "delay" parameter - I used 480 seconds = 8 minutes) and after this period it kills the charge21.sh script which makes the charging stop.

This way you don't need to wait near the phone all the time until it reaches the charge point you want. I used this script to charge over night and it stopped charging 8 minutes after 100% and was ready for another discharge to ~3250mv.