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2018 Model 3 12V Battery Replacement - DIY Guide Needed!

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Chris P. · rep 0 · May 22, 5:27 AM · 1 replies · solved · Question

Vehicle: 2018 Tesla Model 3 Long Range

Hey everyone,

My 2018 Tesla Model 3 Long Range has been acting a bit strange lately. I've been getting "Service Required" messages on the screen, and sometimes the car takes a while to 'wake up' when I try to open the door or use the app. I did some research and it sounds like my 12V battery might be on its way out.

Has anyone here replaced their 12V battery on a Model 3, specifically a 2018 model? I'm pretty handy and would prefer to do it myself if it's not too complicated. What tools do I need, and are there any specific precautions I should take?

Also, where's the best place to buy a replacement battery? I want to make sure I get the right type. Any tips or step-by-step guides would be super helpful! Thanks in advance!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:27 AM

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ClearTheCode admin answer:

It sounds like you're experiencing classic symptoms of a failing 12V auxiliary battery in your 2018 Tesla Model 3. While the main high-voltage battery powers the drivetrain, the 12V battery is crucial for all the vehicle's low-voltage electronics, including the computer systems, door locks, lights, and even initiating the high-voltage contactors.

Causes of 12V Battery Failure:

  • Age: Like any lead-acid battery, the 12V battery has a finite lifespan, typically 3-5 years.
  • Cycling: Constant charging and discharging cycles, even if managed by the car, contribute to wear.
  • Temperature Extremes: Both very hot and very cold climates can shorten battery life.

DIY 12V Battery Replacement Steps (2018 Tesla Model 3):

  1. Safety First:
    • Park your vehicle on a level surface and engage the parking brake.
    • Ensure the vehicle is "Powered Off" via the touchscreen (Controls > Safety > Power Off). Wait at least 2 minutes.
    • Open the front trunk (frunk).
  2. Access the Battery:
    • Remove the plastic trim panel covering the frunk well.
    • Locate the 12V battery, usually under a cover on the passenger side. You'll need to remove a few fasteners to access it.
  3. Disconnect the Old Battery:
    • Crucially, disconnect the negative terminal first (black cable, usually marked with a minus sign) using a 10mm wrench.
    • Then, disconnect the positive terminal (red cable, usually marked with a plus sign).
    • Carefully remove any hold-down straps or clamps.
  4. Remove and Replace:
    • Lift out the old battery. It can be heavy, so be careful.
    • Place the new 12V battery into the tray. Ensure it's the correct type (often an AGM battery, specific to Tesla's requirements – check your owner's manual or a reputable Tesla parts supplier).
  5. Connect the New Battery:
    • Connect the positive terminal first (red cable).
    • Then, connect the negative terminal (black cable).
    • Secure any hold-down straps and replace covers.
  6. Re-energize and Test:
    • Close the frunk.
    • Open a door to wake the car up. You may need to press the brake pedal.
    • Check for any warning messages. The car might take a moment to recalibrate.

When to See a Shop:

  • If you are uncomfortable working with automotive electrical systems or batteries.
  • If you encounter any unexpected issues during the process.
  • If, after replacement, the "Service Required" message persists or new electrical problems arise. This could indicate a deeper issue with the charging system or other components.
  • While Tesla doesn't use standard OBD-II codes for this specific issue, the "Service Required" message often corresponds to internal diagnostic alerts that a service center can interpret more precisely.

Always dispose of old batteries responsibly at a recycling center.

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