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Unable to power 12V system from battery charger in 2021+ MS LR


Well-Known Member
Supporting Member
Apr 5, 2013
I had appointment today with Tesla Mobile Service to fix non-operational electric door unlatch (manual was opening the door) and charge port door which would not open using a button on mobile connector plug (and couple other even more minor things). While replacing the charge port tech connected the 12V battery to the external charger per the procedure (based on his explanation). He proceeded replacing the charge port without noticing that one of the leads of the charger disconnected, causing 12V to go dead during the firmware update following the installation of the new charge port.

As a result, the 12V is battery dead, and connecting the charger doesn't bring neither the 12V battery nor the aux system to a proper voltage to energize it. So the car is not drivable and requires tow to the service center because mobile techs (the mobile tech working on my car called for reinforcement) could not power the 12V aux system. They say that car needs a tow to replace the 12V battery, but I am concerned that the problem now could be deeper, as I don't understand why connecting the external charger doesn't power the 12V aux system, making the car non-drivable.

Anybody else with a similar problem?
Last edited:
In the transportation section there is information on how to connect to low voltage battery:

ump Starting the Low Voltage Battery​

Model S cannot be used to jump start another vehicle. Doing so can result in damage.
If jump starting Model S using another vehicle, refer to that vehicle manufacturer's instructions. The following instructions assume an external low voltage power supply (such as a portable jump starter) is used.
Avoid short circuits when jump starting Model S. Connecting cables to the wrong jump post, touching leads together, etc., can result in damage to Model S.
  1. Open the hood (see Opening Hood with No Power).
  2. Remove the maintenance panel by pulling it upwards to release the trim clips that hold it in place. Front hood open and the maintenance panel highlighted with an arrow pointing upwards.
  3. On top of the low voltage battery, lift the locking tab that attaches the electrical connector to the connector housing.
    The appearance of the electrical connector and connector housing may vary, but the procedure remains the same.
    Locking tab on top of low voltage battery with an arrow pointing upwards.
  4. On top of the low voltage battery, pull the connector housing to the left. The electrical connector releases from the low voltage battery. Connector housing above low voltage battery with arrow pointing away from the electrical connector.
  5. Release the cover from the red positive (+) jump post, and then connect the low voltage power supply's red positive (+) cable to the red positive (+) jump post.
    To avoid damaging Model S, do not allow the positive cable to contact other metal components.
    low voltage power supply positive cable connecting to positive jump post.
  6. Connect the low voltage power supply's black negative (-) cable to the vehicle in the location shown. Ground location in front of the low voltage battery.
  7. Turn on the external power supply (refer to the manufacturer’s instructions). Touch the touchscreen to wake it up.
    It may take several minutes to receive enough power to wake up the touchscreen.
  8. When external low voltage power is no longer required, disconnect both cables, beginning with the black negative (-) cable.
  9. On top of the low voltage battery, push the connector housing towards the electrical connector so that the electrical connector engages the low voltage battery.
  10. On top of the low voltage battery, push down the locking tab that attaches the electrical connector to the connector housing.
  11. Replace the maintenance panel by placing it back in its original location and pressing down until it is secure.
  12. Close the hood.
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