When you're on the main screen, look at the top screen. At the
top right corner there's this battery icon. That's the
indicator.
But I think it doesn't work leh. Mine is forever green. I think
that battery indicator is just for display. Can somebody confirm
this?
The battery will last 15-19 hours on the lowest settings, and 5-8
hours on the brightest. If you're using R4 or Supercard or M3, the
battery usage is more. I think this can be a rough gauge of your
battery other than the battery indicator.