Fixed it by carefully and gently pushing the tab down by hand and not trying to wedge the second battery in place.So the tab on the gun was pre-bent at an angle where the tab on the head goes straight out. It looks like the tab spacing in the gun is about 9 mm and 10 mm in the head. The tab in the old head was the same way so I tried to push the battery in thinking it was just a tight connection but then it ruined the tab so I am just being over cautious with the replacement head.