My Bangle JS2 battery has gone 37 days and is at 9% now

Sorry - maybe I wasn't clear - what I mean is, in order of power usage:

• Update every minute - by far the best battery life
  
• Update every second, but only update the area where the seconds text is
  
• Update every second, but update the whole screen - by far the worst
  
  

Updating every second will still hurt battery over updating minutes, but it's significantly better than the whole screen. I know some watch screens can take almost a second to update, so in that case the CPU is occupied pretty much all the time.

But for example this code, tried just now, takes around 3.5ms, so isn't going to be so painful at all:

function onSecond() {
  var t = getTime();
  var d = new Date();
  g.reset().clearRect(0,24,100,48).setFont("6x8:3").drawString(
    d.getSeconds().toString().padStart(2,0),0,24);
  d.getSeconds();
  g.flip(); // just to ensure we include the screen flip in our time estimate - not needed
  print(getTime()-t);
}

setInterval(onSecond,1000);

By contrast Anton Clock plus redraws everything and when seconds rendering is enabled it takes around 175ms every second, so obviously is going to be terrible!