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I drive a big battery on wheels. Why do I need the little 12V one?

I drive a big battery on wheels. Why do I need the little 12V one?


Why do EVs still have the old-school 12-volt automotive battery?  It’s an interesting question for sure!  Although an EV’s primary source of power is the high voltage (HV, or “big”) battery, virtually all EVs still have a 12V battery on board - and it’s to power all the accessories that gas-powered (ICE) have too!  Headlights, taillights, power windows, power locks, power mirrors, power seats, audio systems, keyless entry, climate control - everything else electrically powered runs off the 12V system.  


And just like with an ICE engine’s alternator, the HV battery recharges the 12V battery when the vehicle is ‘running’ using a DC-DC converter.  On both the Mustang Mach-E and the F150 Lightning, the 12V is tucked away behind the frunk’s inner panels.


The 12V battery’s function in an EV is very similar to what it does in an ICE vehicle. When you get in your Mach-E or Lightning and press the Start button, the 12V battery performs all the tasks needed to ‘wake up’ the HVB (high voltage battery), and perform all the “preflight” tests to make sure everything is running as it should be. The 12V also runs accessory systems like the windshield wipers, airbags, and other safety systems. The 12V is also responsible for keeping major safety related components (such as the power steering, brakes, and lights) working and powered in the unlikely event the HVB shuts down and you need to safely come to a stop and avoid an accident.


In the event of needing a new 12V, please leave it to the professionals.  Modern EVs and ICE vehicles have a BMS (battery monitoring system) and a few other modules that make replacing the battery quite tricky and not something you can safely do at home.


The “little” 12V battery in your EV is just as important as it is in an ICE car!  And just like in an ICE car, the 12V batteries have a finite service lifespan.  This is why it’s very important to make sure the health of the 12V battery is checked. This is included in the EV Works package offered by Key West Ford Service, and should be done at least twice a year.

Categories: Mustang Mach-E, EVs, F-150 Lightning