12v battery in a Tesla
Yes, all Tesla’s are equipped with a 12 volt battery.
But it isn’t used as a “starter” battery.
The 12v battery is used for lights, computers, windscreen wipers, and other auxiliary systems.
Why use a 12 volt battery instead of the big battery pack?
When the car shuts down, the main battery is completely isolated for safety reasons. It’s the 12v system which will operate the isolation relays.
Furthermore, since most existing cars use 12v for lights, wipers, etc., newer electric cars share many of the same accessories.