Yes, opening the back does remove the water sealant that is factory installed. You might be able to find the replacement “glue” that gives the phone the water proof rating but I’m not sure I would really trust it. Probably easier to just be really careful near liquids after the battery replacement. I’m looking at battery replacement in the next few months and that is my plan anyway, just keep the phone away from liquids like I’ve always tried to do with every phone I’ve owned.