I concur with those above regarding Ecoglow questions:
Does it get warm enough underneath? - Yes, absolutely. Because it's radiant heat, you don't really feel it when you put your hand under, but it is totally great for the chicks.
When to move it up? - I put a small block of wood under one side when my chicks were about 10 days old. It was quite warm for a couple of days then, and I kept finding them splayed out in front of the Ecoglow instead of under it. The weather has cooled since, but the chicks have grown a bit so I think they still appreciate the extra 1/2" of height on the one side sometimes. Most of the time, though, I still see them all together on the lower side. They are 16 days old today.
Putting contact paper on top - It doesn't get warm on top at all. I put rubbery shelf liner on top. When it gets poopy, I just rinse it off and squeeze it out, wipe off the surface, and put the shelf liner back.
Battery: you could certainly plugin it in to a camping battery. But other than that I don't know. I would *like* to know, in case I ever get a power outage...
When the chicks won't need it anymore: I can't speak to that one myself, as this is my first go-round with it.
One thing I've noticed my chicks tended to do when very young was get stuck between the wall of the brooder and the end or back side of the Ecoglow. To prevent this I folded up some extra shelf liner and stuffed it between the brooder and the wall.