Shutdown LCD4 Cape

I have connected a battery to BBB in order to provide safe shutdown on power failure but am looking to find out how to shutdown the LCD4 cape until power is re-inserted.

Currently if I execute a shutdown -h now command, the BBB shutsdown but LCD stays lit (with lots of garble on screen). I have also tried setting brightness to zero by writing ‘0’ to backlight brightness variable (in device tree) but this doesn’t blank the LCD (it dims, but not blanks).

Short of adding a switch controlled by GPIO I’d like to see if there is s/w only solution to shutting down LCD.