After tinkering around with it for a while I was able to identify some issues with it.
Some of them are an easy fix, others will require some more attention.
The good news is that the main functionality (charger IC) appears to be working just fine so I was
able to write a micropython driver for it (see here).
The driver needs to be built into the firmware as a frozen module because of memory reasons.
The bad news is that the I2C level shifter and the MPPC IC are not connected in the way they
should be but I might be able to fix that with a bit of hot air and a steady hand.
I was also thinking about writing a proper Tasmota driver as well since I think it is a device that fits
well into that ecosystem. However I have no experience with the Tasmota API so that might
take some time...