The label on the mattress
There is a label on all mattresses sold in the U.S. that says "Do not remove under penalty of law." It does not explain that the law applies only to the sellers, so the label is seldom removed by the owner. It has become an American joke, alluding to the unreasonable fear of breaking rules.
The point being that, in spite of any warnings, the warranty on a piece of equipment would never be voided by any reputable company by removing screws to replace a battery. :)