Some lower end UPS's you can't extend the run time without the circuitry overheating, but larger ones you are generally safe.

We just hang lanterns from the ceiling lights, kids think its fun. When we visit Amish country we notice that all the houses belonging to the Amish look juts like our houses now, the only way to tell them apart is at night the Amish will have an LED lantern hanging in the center of the living room instead of the normal lights we are used to. We basically do the same, just hang one up like that.