Why do you have to remove the entire mount? You can leave the mount in place and just remove the FFII using the two screws on top of the sight.
If you have a vise, lock the gun in a vise, sight on the wall across the room. Mark the spot on the wall where your dot is, then remove, change batteries, replace and check you sight to the marked spot on the wall.
I also like the bird shot at 10-15 yards if you don't have a bench vise.