I tried using event instead of the 25ms underglow_tick to update the underglow on
layer change only. That didn't improve the battery life much....
The second change is cutting off the led strip power if the underglow is
not defined for a layer. Power is restored if a layer with rgb is
activated, and cut off as soon as the layer is disabled.
This, on the other hand, improves the battery life a lot, especially if you
don't use rgb on your base layer.
If you are using rgb on your base layer, setting
CONFIG_ZMK_RGB_UNDERGLOW_AUTO_OFF_IDLE is highly recommended.
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