Are there any battery powered grow lamps?

You can find LED grow lamps at your local big-box home improvement store. They aren't huge like most grow lamps, they do work, and they only draw like 30 watts each. Your landlord wouldn't even know they were there unless he looked.

Now, if you are growing 100 pot plants, you'd need about 100 of these, and then they would show up on your electric bill. If you are only growing a half dozen, they don't use enough power to cause a huge spike in the bill.

They also don't cause nearly as much heat as the huge lamps, another plus.

No. If there were, their batteries would probably have to be as big as a refrigerator. Or bigger.

Can't you just show them what you are growing?