Aqualand Diver 200 m
Taking a picture of the opened watch before changing the battery
is a good idea. Like in this case, the battery covers are sometimes real artworks and not so easy to be replaced after the battery change. If you use this watch for SCUBA diving, please have the battery exchanged at an Authorized Citizen Service Center and insist that the watch is pressure tested afterwards.
What I normally do is to replace the o-ring if I think its elasticity suffered and I also lubricate the o-ring with a bit of watch silicone. That can be bought at any watch parts shop and costs very little. I normally put a small amount on my thumb and index and then carefully pull the gasket ring through my fingers. A big blob of silicone could discolor movement parts if it were to end up inside the watch.
Recalibration after a battery change