automated brightness switch battery - mains

[tpprynn]

I'm using the 64 bit Cinnamon edition of Debian 10 on both my laptops. They both have strong battery life but I would ideally have them use 30% brightness on battery and 90% when plugged in. The power manager as supplied seems quite minimal. Obviously it's no hardship to alter brightness manually but if there's a simple enough way to automate this as described I'd like to. Is there a script I could see, or is there a replacement power manager that would work, or another option I haven't considered? I am merely above average with my grasp of the nuts and bolts of tech and can just about imagine a script that reads whether the power adaptor is present and alters the relevant number in /sys/class but am stumped as to the finer points of the commands needed.

Thanks for any hints.

[Head_on_a_Stick]

I think xfce4-power-manager can do what you want.

If not write a udev rule: http://www.reactivated.net/writing_udev_rules.html