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2017 Model S 12V Battery Warning & Phantom Drain

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Mike T. · rep 0 · May 22, 5:21 AM · 1 replies · solved · Question

Vehicle: 2017 Tesla Model S 75D

Hello fellow Tesla owners,

I'm having some trouble with my 2017 Tesla Model S 75D. Lately, I've been getting a '12V Battery Needs Service' warning on my screen, and the car sometimes struggles to wake up or even go into drive. I've also noticed a significant phantom drain on the main battery when the car is parked, much more than usual.

I know the 12V battery in Teslas is crucial, even though it's an EV. Could a failing 12V battery cause this kind of phantom drain on the main pack, or are these two separate issues? I'm trying to avoid being stranded.

Has anyone with an older Model S experienced this combination of warnings and drain? What was your solution? I'm wondering if I should just replace the 12V battery myself or if this indicates a deeper problem that needs Tesla's attention.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:21 AM

0

ClearTheCode admin answer:

Your 2017 Tesla Model S 75D displaying a '12V Battery Needs Service' warning, combined with difficulty waking up and phantom drain, are classic symptoms of a failing 12V auxiliary battery. This is a very common issue in Teslas, especially as they age.

Here's a breakdown of what's happening and what to do:

  1. Understanding the 12V Battery's Role:

    • Even though Teslas are electric, they still rely on a conventional 12V lead-acid battery (or sometimes a lithium-ion equivalent in newer models) to power all the low-voltage systems. This includes the computers, lights, windows, door locks, and the contactors that connect the main high-voltage battery. The main HV battery charges the 12V battery as needed.
    • When the 12V battery fails, it can't hold a charge, leading to the main HV battery constantly trying to recharge it. This constant charging is what manifests as 'phantom drain' on your main battery pack, as energy is being siphoned off to keep the failing 12V battery topped up.

  2. Common Causes:

    • Age: 12V batteries typically last 3-5 years. Your 2017 Model S is well within the age range where a replacement is expected.
    • Internal Failure: Over time, lead-acid batteries degrade and lose their ability to hold a charge.

  3. When to See a Shop (or DIY):

    • Immediate Action Recommended: A failing 12V battery can lead to a 'brick' situation where the car won't wake up or start, leaving you stranded. Address this promptly.
    • DIY Replacement (with caution): For many Model S owners, replacing the 12V battery is a manageable DIY task if you're comfortable working on cars. There are numerous guides and videos available. You'll need the correct replacement battery (often an AGM type) and basic tools. Ensure you follow safety precautions, including disconnecting the HV battery service loop if specified for your model year.
    • Tesla Service: If you're not comfortable with DIY, or if the issue persists after a 12V battery replacement, schedule an appointment with Tesla Service. They can replace the battery and also run diagnostics to ensure there isn't an underlying parasitic draw from another component that's prematurely killing the 12V battery.

Replacing the 12V battery is the most likely solution to both the warning and the phantom drain in your case.

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