Although EVs are powered by lithium-ion batteries, in many cases, EV on-board computers and their power relays are powered by a 12V lead-acid battery and they make the EV safer to use. Things are constantly changing, but for now the 12V lead acid battery lives on in today’s EVs.
Also the separation of two battery types allows the vehicle to safely disconnect the high voltage from the low voltage when the vehicle is not being driven. PulseTech and Pulse Technology assist with this.
For more info, see THIS ARTICLE from Car and Driver.