@ckuehnel After reading the Data Sheet for the charging IC on the PowerC module, It is triggering the low load cutoff. The M5Stick draws only about 10-20mA and I think the shutoff threshold is 100mA. I'm currently fixing the PowerC example code since the current and voltage calculations aren't taking into consideration that the data is a 14bit two's complement number when converting to 16bit signed.
I'm looking at ways to keep the PowerC turned on and two come to mind. One would be to turn off/lower the auto shutoff threshold. Some problems with this are that if the M5StickC shuts off, it leaves the pack on indefinitely or goes below the recommended threshold of 100mA which could cause the pack to fail to shutoff due to drift in the current measurement or turnon randomly. I think at least disabling the shutoff might be worth it if using the StickC in an always on role or Deep Sleep with periodic wake ups from the RTC. I'm not sure how much power the PowerC uses when the StickC is asleep.
The other idea I'm playing with is to set a periodic interrupt to repeatedly set the Low Load Shutdown Timeout to the max value. My thinking is that it might reset the countdown timer for shutoff every time you update it... That way if you turn off the M5Stick, it'll allow the powerC to shut off. I'm currently writing the code, so I'll let you know how it goes.