Even in the latest generation of electric cars there is still (at least) a 12 Volt battery that continues to perform its role. And this is where the question arises. Once the large array is there, what does it need?
In the first place, a purely electric vehicle also has secondary energy supply needs in addition to the obvious one that is for its movement. The latter is ensured by lithium-ion batteries. But for the operation of the sound system, the indicators, the wipers, etc. it does not need a voltage circuit up to 800 Volts, as it is now present in some of these cars.
Nor would it be possible to have this specific, suitable circuit for all the electrical and electronic systems of the vehicle for various reasons, with the safety of passengers being the most prominent.
The electronic unit of each system gets energy from a low voltage battery and there is a different circuit which is autonomous from that of the high. This separation allows the disconnection of the high voltage circuit in case it is required, for example when the vehicle is immobilized due to a fault or after a collision.
In such a case, none of the passengers, bystanders, roadside assistance officers, police officers or rescuers would want to be confronted with (possible leakage from) a 400 Volt or 800 Volt circuit, approaching the car.
Another factor in maintaining the twelve-volt battery in electrified or pure electric vehicles is the fact of standardization. All manufacturers-suppliers of the various systems present in a car know how to make them operate economically and reliably with low voltage.
Any change would require money for research and development, diversification in the production process, etc. For example, if a Plug-in Hybrid or electric vehicle emptied the 12 Volt battery, one can easily connect it with cables to the equivalent of another vehicle and get power, which could not be done if it was lacking.
For now, 12 Volt batteries appear to be still present in new technology vehicles. However, we do not know for how long yet. This is because some companies, such as the Hyundai-KIA Group, have begun to look for a way to connect the car’s low-voltage power systems to its basic batteries.