Just have a busy weekend. We start testing a new prototype.
The power will not be interrupted when you pull out of charging cable. It's a UPS now.
We can get battery level through i2c. RTC works fine but the timed boot function is unstable. Some hardware bugs need to be fixed.
A button is connected to GPIO.7 of pi zero, for soft shutdown or custom functions. However, we just find a GPIO pin provided but powerIC chip... which is a good news. Maybe we should connect the button to the powerIC, and detect it via i2c. Save one GPIO pin!
Using special pogopins to connect the pi, the new version will be as compact as the old ones (or even thinner?). Anyway, we insist on the compatibility with all pi zeros whether it has gpio headers. Just plug and play.