Maybe because the charging voltage is not constant DC but high frequency pulsed?
Naw, these lipo charger ICs are basically cc/cv (constant current then constant voltage near the end of the cycle, maybe with a low input precharge stage) not pulsed or sinusoidal (much more complex/expensive control methods usually reserved for high power and high efficiency systems like electric vehicles, smart grids, etc). USB and the micro Vcc are isolated by design. The usb input voltage powers a regulator in the atmega (to be decoupled by a 1uF cap according to the datasheet) to generate 3.3V to bias the D+,D- I/O and nothing more (although you could tie Vusb to Vcc if desired, which I’ve done on occasion to make batteryless devices that just run on usb power).
Exactly if all I’ve done is bypassed a switch that works (the system runs with a battery).
There’s some witchcraft involved
I should have checked the datasheet
Aha! somehow I never looked good at that part of Arduboy schematic. I somehow thought it was tied to Vcc as in one of the datasheets examples.
Eh. Kinda want to strip it and keep it as a card