Battery Calibration Concern [Bangle1]

In the settings.js app its written to use pin D3, which is the voltage pin for the Bangle.js 2, is it fine to use that one for the Bangle.js 1 too, or should it be using D30 in the code?

Okay so its only enabled for bangle.js 2 at the moment. Is there any reason? If it does nothing for Bangle 1, then it shouldn't be visible in the settings.

I am a complete electricity newbie, but I wanna see if anything I type makes sense.

I been researching the AnalogDigitalConverter workings and a bit of resistor math. If I do analogRead(30) for a full battery I get average ~0.63 and for an empty battery ~0.50. So the battery is a 3.7V lithium battery, that can reach 4.2V when fully charged.

The number analogRead() returns is relative to 3.3V, where 1 = 3.3V and 0 = 0V. I looked at the source and nrf docs to confirm it. So D30 pin :
0.5 * 3.3 = 1.65V for empty battery
0.63 * 3.3 = 2.079V for full battery

So now Voltage Drop between source and D30 when full:
4.2V - 2.079V = 2.121V

Then I assume that the watch stops working at around 1.7V because it says so on nrf docs, so:
1.7V + 2.121V = 3.821V

Thus is it true/valid to say that the battery cycles between 3.821V and 4.2V and the nrf chip is running on between 1.7V to 2.079V to operate the Bangle from empty to full or is that that a load of hogwash.

I think its interesting to note how close 1.65v is to 1.7V
and how close 2.079V is to 2.121V.

I think the original numbers from D30 are the operating chip voltages, and so its slightly under 4.2V when full, and slightly less than 1.7V when empty.

If any of the above is true, it also implies that the full capacity of the battery isn't being used, because the resistors are too strong? I mean in the sense that 3.8V isn't close to being fully discharged, they say its closer to 3V. But on the positive side it would mean that the battery voltage stays healthy, thus ensuring longer lifespan for the battery.

Okay so its only enabled for bangle.js 2 at the moment.

Ahh, oops. I've just disabled the option for Bangle.js 1 users.

Is there any reason?

Just that Bangle.js 1 never seemed to have big issues (I guess they used better resistors). I feel like "If it's not broken don't fix it" :)

There's a voltage regulator to take the battery voltage down to 3.3v, so generally the processor runs on that. I believe the watch usually stops when the battery protection circuit cuts in for low voltage, rather that because the processor browns out.

The processor can't read voltages above 3.3v (it would damage it) so a potential divider drops the voltage (I guess in the Bangle.js 1's case it halves the voltage so 4.2v -> 2.1v).

Interesting. So if it's halving, it still suggests that the watch turns off when the battery is at '(0.5 * 3.3v) * 2' volts? Oh. Now it's making sense!! So it turns off at 3.3v. Thanks!