I Just converted my townie battery rack to dual battery as well. This time I took a few pictures as I went along before adding the batteries so things could be clearer to understand.
First I placed two battery plates back to back and added two bolts at the top. Make sure the plates are oriented so the battery slides on from the back. The these bolts will rest on the rack itself preventing it from sliding down when tightened.
Then I tightened them up just snug enough so they do not slide and added two more bolts at the bottom. You have to make sure you don't tighten them to much as they will reshape the plates and make it more difficult to slide on the batteries.
Then I did the other side the same.
The plates I use are the none rattle type and very difficult to slide the batteries on and off the first few times. If the batteries are slid on and off enough eventually they will loosen up and rattle anyways. The top plate I used is the old style that still works well but the battery does rattle. I call that the "Guest" battery plate and use it for testing other batteries or taking along an extra for a longer ride.
Gary
