no idea what happened, I refrained from doing anything to the main board - but it does no longer charge a battery.
I tried a few different ones at different voltages and capacities (3.3V, 3.5V, 3.8V, 850mAh, 2000mAh) but the charging light does not light up anymore (and its not charging too

All I did lately was adding the fan. It was done quite cleanly and measuring it shows no issues - it also works as expected. I tried desoldering it without effect.
Any idea what went wrong?