I followed with patience the instructions, but trying to calibrate Nybble was impossible, sometimes with "c" command, Nybble moves erratically.
Finnally i tried the solution suggested by Rongzhong Li: "Connect the jumper wire SW3 between BATT and V_S." and this seems to solve all the problems.
I hope this can help someone, because i spent some days trying to know what was the problem, some wrong build/config step, the batteries. (Im using GTF 14500 Li-ion 3,7 V 2800 mAh https://es.aliexpress.com/item/1000004324121.html?spm=a2g0s.90423126.96.36.1999163c0uv9XO3)