I'm quite new to the Pi world, but I need a UPS unit to power both a Raspberry Pi 3B and a 2.5'' hard disk used by the Pi. I thought a power bank could be the right choice for me, but I cannot find a good one with 2 usb port with pass-through feature. If it would be the case, would it be a good idea to have a power bank on charge 24/7? How much impact would it have on the power costs? Of course I'm also open to something different from a power bank as UPS.