BUT, I am unsure about the battery life. does anyone here own one? How long does it last in normal usage? Both with and without GPS (if that can be turned off)
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Don't own one, but it will definitely vary a lot based on what you enable/use or not and your usage patterns (how long you wear it, how much you move...).
The specs say:
350mAh battery, 1 week standby time
- Idle, accelerometer on 12.5Hz - 0.35mA
- Idle, accelerometer on 1.25Hz - 0.15mA (default if not moved)
- BLE Connected in high bandwidth mode - 0.5mA
- Compass on - 2mA
- Heart rate monitor on - 2.5mA
- GPS on - 30mA
- LCD on - 40mA
- Turned off - 0.08mA (0.6mA if turned off via Bootloader)
This means that when idle (in the normal power-on state) you can expect around 30-90 days of battery life depending on whether Bangle.js is moved or not.
So on one side 7 days, on the other 30 to 90 days, and that's for "standy" or "idle".
Obviously the GPS is a killer. 30 mA means the battery will hold less than 12 hours with it enabled.
Likewise the LCD draws 40 mA, less than 9 hours.
In the best case (idle with the accelerometer on the slow setting and nothing else — no GPS, no BLE, no compass, no heart rate monitor, no LCD...) it's only using 150 µA, so it should indeed last > 90 days. But as soon as you wear it and use it that drops pretty quickly.
Worst case (everything on), it will last about 4 hours.
So I suppose that with a combination of standby and activity and depending on what you turn on or not, as well as specific settings regarding when and how long the screen is turned on, it probably lasts about a day in real life.
This review says about 3 or 4 days. YMMV.