I have 2 of the AA taillights. I just toss both of the battery packs into the water bottle holder of my Topeak MTX DXP trunk bag. I haven't had a problem with the batteries popping out of their holders. I just put the batteries in the black plastic holders, put the batteries/holders in their small nylon pouches, and put the pouches in the water bottle holder. I don't think it's necessary to put a rubber band or velcro strap around the batteries, but I guess it couldn't hurt for some extra peace of mind.