Minimizing power consumption

Honestly, when you're wearing the watch the accelerometer power consumption isn't the biggest worry - you're looking at 0.4mA, which is still over 800 hours (30 days).

What kind of battery life are you seeing?

The biggest issue is the time the screen is on (when it's drawing 55mA!) - so I'd say in settings, disable wake on twist/etc, and also wake on BTN2, and maybe lower the LCD timeout. Then the watch will only turn the screen on if you press BTN1 or 3, and is harder to accidentally get into the launched.

If I decrease rate of poll interval would that benefit me?

Not noticably...

Why can't we have a setting in the menu that is power save mode all the time, not just when idle (not moving)?

It would affect other apps/widgets and things like step counting - and as above, the difference isn't actually that big.

Is the poll interval adjustment the only way to save power?

As above - LCD is by far the biggest power draw (or if you've enabled an HRM app that'll draw a bunch of power).

Which javascript api/execution of an app prevents low power mode, is it just any use of setInterval because its then constantly doing something? Can it only save power when its in ClockFace doing nothing?

It's always able to go into low power sleep modes inbetween timers - so having a 1 second interval isn't going to hurt power consumption too much (I just tested, and it's like 0.02mA or something very small). You want to avoid going much faster that that though - and also avoid drawing stuff to the LCD if it's off.

Why isn't disabling accelerometer in the options too? Is it recommended to disable accelerometer if not using it for anything?

It's just that wake on twist/step counting/gestures/etc rely on it. There's also code that kicks watchdog timers, handles the BTN3 reset/etc that needs to run too. While it could be slowed down it can't be stopped.

I guess if you were trying to make the Bangle last multiple months between charges - or maybe set it up to be solar powered or something then turning off the accelerometer and polling would be handy, but I think for most people the difference in power usage wouldn't really be noticeable.