I meant the battery icon that's in the same area as time/clock and signal strength. When you go from using a fullscreen app to a normal app, which changes the meter from not visible to being visible, it usually gets an update.

Of course when you unlock phone to turn on screen, the meter also becomes visible and is updated.

My best advice on script would be to ignore/discard values from hal identical to previous value.

Have you looked at existing battery logging apps such as battery-eye?