Service tech. I am fortunate in having a very good local independent pro camera repairman who is also a friend so I do nothing myself. He just replaced the actual contact / switch with another one from a parts camera that one of his repair buddies had. So there was not even a charge.
Now I carry my ZI camera with a grip in my hand, sometimes for 8 hours. Bags and straps do not work well for me. And I live and photograph were we sweat a lot during the summer. So there is continuing potential for sweat running down my arm / hand onto the camera.
But all battery drains are caused by some weak short circuit and corrosion is the most likely culprit.