Just found this thread after digging through my notepad, finding a sketch from the time just before the forum disappeared. I was on the old thread, but none of the later posts were recovered. However back then I had tried to find the circuit around the embedded MSP430 controller that handles the power and charging:
I remember there were some weird effects when switching the device on and booting OpenWRT - you just couldn't switch it back off without detaching the battery.
The slider switch "Router <-> OFF <-> charger" is connected to a MSP430 Microcontroller (Pins 9/10), just as the two LEDs (Pins 18/19) and the bq24195l battery charger (i2c, Pins 14,15).
MSP430 connects to MT7620 via UART (MSP430 Pins 3/4, apparently 4800 8N1), but I couldn't make sense out of the communication protocol yet.
The binary that handles communication to that chip in the stock firmware seemed to be mcuinfo_cdm56cdl, but I don't have the tools and skills required to reverse engineer that properly to find out how to talk to it (so we could at least shutdown the device, maybe even read the battery status):
So, is anyone still on this? I have a device to test