Like LittleArrow states below, there is a barrel type plug (single) that attaches to the underside of the camera. In the battery case, there are (2) leads running from this plug, a red and a black going to the positive and negative spade terminals on the 12v Sealed Lead Acid Battery. I have not changed these or messed with the polarity of the batteries at all. Like I said, even when I interchange the battery packs, none of the cameras work with the external packs, but they all work with internal alkaline batteries. Ironically, all (3) worked in September when I put them in the field and all stopped working within the few weeks within a few days of one another. I am getting current from the battery pack into the camera but for whatever reason they will not work without batteries. Very strange.