There is a display of battery charge top right in home screen.

Have a recharge log to establish the health and the user behavior. Build an estimation of health and battery life like iPhone does. Just sync according when user suppose to have data available to be checked.

And get a warning when running low ?

That is very important as it mentions to not over charge or undercharge your ring, however we have no way of telling.

I agree I am new to Luna and that would be a great feature.

excellent idea, maybe as a widget or in the persistent notification