I'm not going to draw free-body diagrams for you. If you can't figure out that the shear is being taken out between the battery and the tray, no diagram will convince you. Yes, the battery's CG is above that mounting plane but, rocking of the battery turns into a large vertical translation with only the tiniest lateral translation. If the nuts are tight, that lateral translation is zero. This is how people can have a $100K seat of Nastran and get hyper-accurate, yet incorrect results. Perhaps explain how a rubber strap over the same tray would hold the same battery in place? The rubber strap has no meaningful resistance to bending. Is it magical, non-bending rubber?