I suppose you could just use a digital 110volt timer. I haven’t given it much thought to be honest.
Any touchscreen I mount would use a POE to usb/lightning adapter. If the injector for the POE is on a timer you could set it up to charge every 2 or 3 days for a few hours. Depending on how long the batteries actually last.
On on a side note, Apple seems to feel the iPads can be plugged in I definitely. The OS is supposed to manage to changing and even turn it off if necessary. Obviously this hasn’t worked for everyone!