Show automatically "battery low" warning

Any better way to do this yet? I tried to recreate the first option but it doesn’t make any new sensors.

Is there a way to hide the card when no batteries are under 20%

You can use the visibility tab of the card to add conditions when the card should be visible. I used the same logic in my auto entities list to figure out if any batter was below 20%. If that was false, the card isn’t shown at all.