I only have 5,427 miles on my 2018 Tesla M3, LW, AWD purchased new in Oct 2018. I have a few questions about the 12 volt battery. I still am using the original.
The following comments are correct AFAIK. Since you have low mileage on your 2+ year old car, the 12V battery has probably seen many more charge cycles than the norm; therefore, there is a chance it might be nearing the end of it's useful life.
I recall there are a couple of wires below the right side of the left headlight (driver's side) under that round cap. I know those are to activate the doors and such if the 12 V batteries dies. I think I heard somewhere that all it takes is a little 9 volt battery to activate so the doors can be opened--and I assume drive with a dead 12 volt battery as then the DC2DC converter will supply the voltage from then on, while driving. I am surprised to hear the DC2DC converter is not activated also while charging.
The wires behind the tow hook cover only open the frunk to give access to the 12V battery area. Tesla made a firmware change several months back that disallows opening the frunk,, via the tow hook wires, when the 12V battery is functional.
Anytime the car is awake the DC-to-DC converter is operational. In fact, you can disconnect the 12V negative cable anytime the car is in the awake state and everything works fine (you will get a message on screen that the 12V battery is disconnected). The 12V battery is required to close the HV contactors to transition from the sleep to operational awake state.
Is it really possible to use a small 9V battery there? If so, I guess I should keep one in my pocket!
Yes, last time i tried it. Maybe someone else who has tried it recently can confirm?
Another question is it worth it to install the
Lithium 12 volt battery for $479.00?
And does the warning usually come on before the battery dies? I had no idea there was such a warning until I read this thread.
So when I am I mostly likely to need to replace this battery?
-Don- Reno, NV