12V: Low-Voltage Accessory Battery
The standard lead-acid or lithium-ion battery used to power an EV's lights, infotainment, and safety systems when the high-voltage system is offline.
Deep Dive
Even though an EV has a massive high-voltage battery, it still relies on a small 12V battery to 'wake up' the computer systems and close the high-voltage contactors. If the 12V battery dies, the car is effectively 'bricked' and cannot be driven or charged, even if the main battery is at 100%. This is one of the most common causes of EV roadside assistance calls.
Common Symptoms
- Key fob not detected
- Infotainment screen flickering or dark
- Doors failing to unlock
- Vehicle failing to enter 'Ready' mode