I was doing some general maintenance on the board and I had to charge the battery from my lab bench power supply so I can finish in time for a ride. I noticed the battery lasted longer than usual so I looked at the controller pcb and noticed there’s a diode between the charger and the battery. That diode has a Vdrop of about 0.58V at 1.5A charge current, and around 0.4V at 100mA (which happens towards the very end).
That means that the battery is getting a max of 41.6V which would not charge the batteries to their max capacity. Ideally you’d mod the charger for 42.4V output but I’m not sure how easy it is. I’ll look into it at some point. The switchmode controller usually has a two resistor divider that senses the output and usually you could parallel a resistor with one of the two to slightly increase the output voltage, but I need to confirm this.
The Vdrop at higher current doesn’t matter, because if the current drops so does Vdrop, so then it’s a kind of self regulation. What matters is the Vdrop at the lower current towards the end as that caps the max voltage the battery sees.
Maybe someone finds this useful. You can try it by charging your battery off the board using a lab bench power supply and see if you notice increased range.