The duck. My reason being that ducks have full vision while bats don't. Take a look at this one:
This is a Muscovy duck. Males can easily get to over 27lbs. They don't fly, but they have VERY large talons to climb trees. Also, they don't quack like other ducks, they have a unique hiss.
The bat of course. A duck wouldn't attack a bat. Even if it could, it couldn't get anywhere NEAR the bat. The bat would attack in night when the duck is sleeping. And the duck would panic. Ducks don't eat bats. Yes.
the winner would depend on what time of day it is if it where the day the duck would win but at night the bat would dominate. But if I had to pick I would say the bat cause bats would strike at night.
Normally they would have nothing against each other, but if they did, I don't think the bat would have any weapon but his fangs and unless they were a vampire bat or had poison, the duck would win.