Originally Posted by KRSW

If you do decide to do this, I'd suggest disconnecting the batteries, and on the smaller units, taping the battery terminals. Quality units usually have a physical disconnect switch/plug on the back of them. While lead-acid batteries aren't anywhere near as bad as LiIon batteries in acting badly, it still can happen. Likewise, you don't want the UPS randomly turning itself on while it's in an enclosed space and overheating. Fire on an aircraft is a very bad thing.