Best method to turn off ps5 controller?

Putting the console in rest mode turns the controllers off too. If you're done for the night, that's the one button.

Hold the PS button for about 10 seconds and it shuts off. Or press it once, go to accessories in the control centre and turn it off from there. If you're doing this because it keeps draining while you watch stuff, set the auto-off timer in the power saving settings instead, saves you thinking about it.