Preheat a deep fryer or Dutch oven with 3" of oil to 375 F.
In a medium bowl combine the tempura mix, onion powder and pepper.
Stir in the water.
Add most of the beer and stir. You want the batter to be like pancake batter but thinner. Add more beer if you need to make it thinner. If you end up adding too much liquid just stir in some more tempura mix to thicken it.
Working in batches if needed, dip the rings into the batter and place in the fryer.
Fry 3-5 minutes, flipping once, until golden brown.
Transfer to a wire rack or paper towel-lined plate to drain.