That's a good question! Generally, when a phone manufacturer designs a phone to be waterproof, they use seals and adhesives to protect the internal components from water and dust.
However, ***opening the phone to replace the battery can compromise these seals.*** Even if the battery replacement is done carefully, it's very difficult to guarantee that the original waterproof seal will be perfectly restored.
Therefore, ***it's likely that the phone will no longer be truly waterproof after a battery replacement.*** It might offer some level of water resistance, but it's best to avoid exposing it to water or liquids to prevent potential damage.
If maintaining the phone's waterproof capability is crucial for you, it might be worth considering professional battery replacement services that specialize in maintaining water resistance, although even they might not be able to guarantee it completely.