You just don't know it yet

It's been shown that mirrors can reflect spells. The Mirror of Erised (from the first book) can reflect a killing curse, but I'm not sure if that's particular to that mirror or if all work. With a bit of experimentation, Bats could probably find a way to produce a powerful enough reflecting object to at least temporarily disable Voldemort. He would definitely have little problem dodging attacks.

But he gets the Batcave and four days of prep time.