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2018 Model 3 12V Battery Failure - Car Won't Start!

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Mike T. · rep 0 · May 25, 4:04 AM · 1 replies · solved · Question

Vehicle: 2018 Tesla Model 3 Long Range

My 2018 Tesla Model 3 Long Range, with about 75,000 miles, completely died on me this morning. I got into the car, and nothing. No screens, no power, just a dead vehicle. I tried opening the doors with the app, but it was unresponsive.

After some troubleshooting, I managed to get a jump start from a mobile service tech, and the screen came alive with a '12V battery needs service' alert. Is this a common issue for older Model 3s? I thought the main battery powered everything.

What's involved in replacing the 12V battery? Can I do it myself, or do I need to schedule a service appointment? I'm a bit frustrated as I didn't get any prior warning.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:04 AM

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ClearTheCode admin answer:

It sounds like you've experienced a common issue with the 12V auxiliary battery in your 2018 Tesla Model 3. While the main high-voltage battery powers the drivetrain, the 12V battery is crucial for starting up the car's computers, lights, windows, and other low-voltage systems. When it fails, the car essentially becomes a brick, even if the main battery is fully charged.

Here's what you need to know and do:

  1. Causes of Failure:

    • Lifespan: Like any lead-acid (or newer lithium-ion) 12V battery, it has a finite lifespan, typically 3-5 years. Your 2018 model is right in that window.
    • Constant Cycling: The 12V battery is constantly charged and discharged by the DC-DC converter from the main high-voltage battery, which can lead to wear.
    • Software Glitches: In some rare cases, software issues can cause excessive drain or improper charging of the 12V battery.

  2. Replacement Process:

    • DIY vs. Service: For earlier Model 3s (pre-2021), the 12V battery is a lead-acid type and is generally accessible under the frunk. Many owners with some mechanical aptitude can replace it themselves. You'll need basic tools and a replacement 12V battery (Tesla-specific or compatible aftermarket). Newer Model 3/Y vehicles use a Lithium-Ion 12V battery which is more complex to replace and often requires service center intervention.
    • Safety First: Always disconnect the main high-voltage battery before working on the 12V system to prevent electrical shock or damage. Consult your owner's manual for the exact procedure.
    • Warning: If you're not comfortable with electrical work or working around high-voltage systems, it's always best to schedule a mobile service or a service center appointment. Tesla service can replace it quickly and ensure all systems are properly reset.

  3. When to See a Shop:

    • If you're unsure about performing the replacement yourself.
    • If the '12V battery needs service' alert persists after replacement.
    • If you notice any other unusual electrical behavior or error messages.

While there isn't an OBD-II code for a dead 12V battery, the '12V battery needs service' alert is your primary indicator. It's a critical component for vehicle operation, and proactive replacement around the 3-4 year mark is often recommended by experienced owners.

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