I charged my M5StickC to full and flashed a blinky sketch. It's been working just fine (including console log of the time) for hours now.
Have you tried charging yours fully?
It would be nice to get some bindings with the AXP192 though, as it also controls the backlight of the LCD :P It's using the st7735 but without the backlight getting power, we can't see anything on the screen (or at least that's what I think; maybe I'm just using the lcd wrong).
Would also be nice if we can somehow get something like https://www.espruino.com/Reference#l_NRF_getBattery working through the power management chip :P