I setup a USB breakout board with 5V & GND and nothing on the data lines to see what battery powered USB devices I could find that would still charge. I was expecting to need at least some resistors on the data lines but so far everything I've tried to charge has worked, even a few USB-C phones. So now I'm scouring house looking for any other devices to test to see if it won't charge.
I was looking to order some charging port ICs for testing but looks like these will not be necessary. Simple mosfet to switch top off each device periodically will keep things simple and cheap.