There is no problem here, it goes and works for me. It comes from this "blue" 36V wire from the display. I gave it through the diode, because the signal also goes to turn on this stepdown and I preferred to separate these two circuits with diodes.
Thanks, I'm writing with you, by the way, I saw on Ali 18650 50000mAh 10pcs for 120 PLN, two such packages and BMS 10s for about 45 PLN, plus plastic for grouping, e.g. 10s2p and for my 36v 350W drive and 36V 16A controller, it gives it's almost 300km on a single charge, ok maybe you would have to buy a 42v 4A charging adapter for 80 PLN, because the one I have for 2A will land for a long time, but the calculated range gives food for thought, did you do it?