Homeowners with powerwalls or similar will have the same issues in floods. I would never have one of those in my house. Outside well away from house, maybe.
The Powerwall 3 has a thick metal shell and the front is glass sealed with o-rings and screws that are single use because of water-tight silicone sealant as well. The metal shell can rust quickly (I’ve seen one with tape on it rust under the tape within days of first rain after water got under the wrinkled tape.) If Musk is smart he will try to one-up the Chinese EV company that is running videos of one of their EV Land Rover wannabes roaming around a lake and make the Teslas and batteries waterproof in the next iteration or even this one. The hurricane will dampen their sales in the south fast otherwise.
There are lots of videos of Teslas in lakes too. But salt water for days is a harsher environment than fresh water for hours.