The Bangle's got a LiPo battery (so yes, around 3.7v, 4.2v when it's just come off the charger)
The value from analogRead is actually the 3.3v reading scaled to the 0..1 range, so 0.293 = 0.97v - which would definitely fit with 1/4 idea.
Resistor/capacitor values are notoriously bad though. Normally you get them with 10% tolerance, but they sell the 5% tolerance (and 2, and 1) for a premium - so if you use a 10% tolerance resistor you're basically guaranteed that it isn't the resistance you ordered, but is at least 5% higher or lower.
With LiPo batteries, that 5% can actually make quite a big difference in what's reported.
It might make sense to add a 'calibration' to the Bangle.js firmware that allows you to charge your Bangle up and then flatten it (just by turning everything on) and use that to come up with an accurate battery usage figure.
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