@etolocka Well, Ernesto, if the returned value is saying that the battery is 100% of 4.2 volts...I think you are THERE!
I do not use Python, have a board like yours or ever monitored battery voltage, so I am no expert, it looks like you are OK!
hmmm...I am way out of my depth here.
The PeakCan seems to be CAN to USB.
Do you have an example sketch to base this on?
The ESP32 connects to which end, the USB or CAN?
Does the equipment offer automotive style OBDII communication?
If you have the time, I'd like to know!