Changing the battery does not require re-sighting of the gun, I have had to do it several times.
Word of advice, always carry an extra battery with you to the field, I havae spare taped inside my stock of my mossbery turkey thug. I have gotten to the field on more than one occasion to see the scope gott accidently turned on or left on in the excitment of a shot the day before.
The first thing I do now after loading is turnt he scope on to ensure it is still working to avoid any unexpected surprises