The box is vented to the outside with two 1.5 - 2 inch dia hoses. An inverter / charger is also mounted in that storage cabinet. I really don't want hydrogen gas building up in the compartment. Since the box does not seal by design, I normally wrap a few turns of duct tape around the box. I do have a watering kit installed so I really don't have to access to batteries that often. I just thought there might be a better way of doing this. It is not a round hole in the box, it is more of a slot maybe 1 inch wide 1 3/4 deep with a flat on the top. Just wondering if some one had come across something that was made for that box.