Each robot only knows their own state, but they’ve been asked only about both. So no robot can say “yes”. If a robot needs a new battery, it must say “maybe”, because it knows one or more robots needs a new battery. But if it doesn’t need a new battery, it must say “no”, because it is confident that it’s not both that need new batteries.

I found the second robot’s answer helpful in understanding the situation, but it’s logically not needed to answer the question.