Tesla Owners Encounter Problems with 12-Volt Battery

By · January 22, 2014

Tesla Model S Nose Cone

Access to the Tesla Model S 12-volt battery is through the reflective oval-shaped nose cone.

Tesla claims the 12-volt battery in its Model S should last “a number of years.” But Tesla owner chat rooms are full of discussions regarding 12V battery replacement. Several Tesla owners talked with PluginCars.com about problems with their 12V battery. Rather than a huge design problem, they saw the issue as proof that Tesla is not immune to the same kinds of problems all automakers have with defective parts.

The low-voltage 12V battery, similar to the auxiliary battery found in gas-powered cars, should not be confused with the much larger high-voltage battery pack and related systems that provide energy to the Model S.

Mike DeSimone, a green-tech angel investor in New Jersey, received his Model S in March 2013. A few months later it was dead in his garage. He called the Tesla Rangers and they were able to jump the 12V battery, adding enough power to release the parking brake and drive it on a tow truck. Tesla replaced the 12V battery, said DeSimone. He isn’t sure what caused the battery to die.

Another Tesla Model S owner in Silicon Valley had a more intractable 12V battery issue. The owner, a mechanical engineer, explained: “The problem is that it was plugged in and the DCDC converter didn’t turn on, so the 12V battery died in the middle of a vehicle software update. So I don’t know exactly what happened, but I believe the software update was incomplete when the 12V battery died. So they actually couldn’t even get it running after that. They had to drag it onto the back of a flatbed tow truck…wheels screeching.”

In the Tesla Forum chatroom, 2013 Model S owner StefanT said Tesla called him to tell him “the 12V battery needs replacing and the firmware that controls charging of the 12V battery needs updating.”

User Kleist in the Tesla chatroom explained: “There is a physical connection between the large battery and the 12V battery and it is called the DC-to-DC converter. During my last visit service they updated the DC-to-DC converter firmware. Problem is that the 12V battery controls the main battery switch. If the 12V battery is dead then the whole car is dead and cannot be recharged from the main battery.” Kleist pointed to an EV emergency instruction video, made for first responders and filmed at Tesla Motors, that explains these systems in great detail.

Nothing To Do With Bricks

Tesla’s public relations department took questions from PluginCars.com regarding dead or near-dead 12V batteries very seriously. It also objected to any association of the term “bricking” with a Model S.

After consulting with Tesla engineers regarding the 12V battery problems, Tesla told PluginCars.com that 12V batteries should last a number of years, but “when the Model S first shipped, the 12V battery was cycled more often than desired. This means the 12V batteries in our initially delivered vehicles aged more quickly.”

Tesla offered software updates that reduced the load on the 12V battery when the car was not in use, said the Tesla engineers. “Thus the 12V battery will last significantly longer in all vehicles.”

The Tesla owners PluginCars.com spoke with were driving fairly new models. But maybe the software update hadn’t been installed. Or maybe they just had a bad batch of 12V batteries, suggested DeSimone, who once owned a BMW dealership. “Things happen with cars,” he said.

New to EVs? Start here

  1. Seven Things To Know About Buying a Plug-In Car
    A few simple tips before you visit the dealership.
  2. Incentives for Plug-in Hybrids and Electric Cars
    Take advantage of credits and rebates to reduce EV costs.
  3. Buying Your First Home EV Charger
    You'll want a home charger. Here's how to buy the right one.