Imagine: I have the display powered separately from the RPi (in my case a RPi3). Sometimes, the RPi will have power, but the display will not. This situation might go on for one second, one minute, or ten minutes, but not much longer. Obviously, there will be nothing displayed at that time (duh, it will be black), and touch input won't work.
Here's why. I have my RPi installed in an electrical control box, where it is monitoring (and in the future also controlling) pumps and related equipment. The site has a gas-powered generator, but when the utility power goes out, it takes between 10 and 30 seconds for the generator to come on. Clearly, that's long enough for the RPi to crash. For my server at home, I have a big UPS, but clearly a UPS that's the size of a shoebox is insane for a RPi. So I was toying with the idea of using Adafruit's mode 2465 PowerBoost charger/converter and a small LiPO battery to build a tiny UPS (fits in a small DIN-rail mounted case) that can power the RPi for a few minutes if need be. So far, so good.
The question is: Do I also have to keep the display powered? Will the RPi and the touchscreen functionality go crazy if the display loses power? If I need to keep the display running also, that's not a disaster, it just means that I'll probably need to run a second PowerBoost board for the display and a second battery.
Any input on this?