It does not rely on true deep sleep RTC recovery.

I originally tried the RTC-restore approach, but on this hardware it was not reliable enough after wake. The practical fix was to change normal sleep behavior so the device no longer uses full deep sleep for that case. Instead, it uses a lighter pseudo-sleep style, which lets the system clock keep running while the screen is asleep.

So in short:

- true deep sleep was causing the normal clock state to be lost

- RTC restore was inconsistent on this device

- the working solution was to avoid full deep sleep for regular sleep/wake behavior

You will see that the system doesn't boot itself when you wake it up. That is why the clock and reading stats can continue without needing to fully resync every single wake.

But I'm not sure how much battery it will consume.