One month old 85D - 12V battery bites the dust

Maybe not? I've seen this issue before with people that have left their cars for several days or more. Try charging the car for a period of two hours using your normal charge method, then drive it for 20 minutes. This should help normalize the 12 V energy level. Do this once more if needed, and then continue charging and using the car normally, but also monitor it for any messages over the next week.

I'd drive over and say give me a new battery now. Don't want to risk being stranded. Hopefully some corner of the gigafactory can make a decent 12v battery.

I'm secretly (or not) hoping they have plans to go with the Li-mg 5,000 cycle chemistry that is used in the 7kWh power wall. At equal capacities that would make it at least a 2.5 year battery, at equal volumes a ~6 year battery and at equal masses an ~8 year battery.

I was surprised to see that the +12V battery is not charged when the car is set to Energy Saving "ON" (low power consumption is active) and that the +12V battery can discharge in as little as 12 hrs. (see Note: under Battery Care). It would appear the Energy Saving is dedicated to limiting the energy consumed from the primary battery and leaves the +12V battery venerable to discharge.

It would also seem that continuous use of Energy Savings mode would risk draining the +12V battery if you didn't turn the car back on soon enough.
IMHO, Even the Nightly mode may cause premature battery death if it is used every day. I have yet to find the spec. on this battery type, so I will reserve my judgment.
I anticipate the Energy Savings mode should only be used for a few hours while and when you cannot plug-in and you are at risk of not having sufficient range/charge and you want/need to save the energy in the primary battery.

m6bigdog said:

I was surprised to see that the +12V battery is not charged when the car is set to Energy Saving "ON" (low power consumption is active) and that the +12V battery can discharge in as little as 12 hrs. (see Note: under Battery Care). It would appear the Energy Saving is dedicated to limiting the energy consumed from the primary battery and leaves the +12V battery venerable to discharge.

It would also seem that continuous use of Energy Savings mode would risk draining the +12V battery if you didn't turn the car back on soon enough.
IMHO, Even the Nightly mode may cause premature battery death if it is used every day. I have yet to find the spec. on this battery type, so I will reserve my judgment.
I anticipate the Energy Savings mode should only be used for a few hours while and when you cannot plug-in and you are at risk of not having sufficient range/charge and you want/need to save the energy in the primary battery.

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I think you are referring to two different power saving modes. According to the Battery Care section of the Owner's Manual that you referenced, the "low power consumption mode" begins when the main battery has discharged to 5% or less. In that "low power consumption mode" the Note says that the auxiliary 12V battery is no longer being charged and can completely discharge within 12 hours. That mode is not driver selectable.
However, that "low power consumption mode" is not the same as the driver selectable Energy Saving modes of "OFF", "NIGHTLY", and "ON" located at "Controls" > "Displays" > "Energy Saving". I believe that the auxiliary 12V battery is still being charged whenever any of these driver-selectable Energy Saving modes are selected, assuming that the main battery is charged above 5%.

LineofSight said:

I think you are referring to two different power saving modes. According to the Battery Care section of the Owner's Manual that you referenced, the "low power consumption mode" begins when the main battery has discharged to 5% or less. In that "low power consumption mode" the Note says that the auxiliary 12V battery is no longer being charged and can completely discharge within 12 hours. That mode is not driver selectable.
However, that "low power consumption mode" is not the same as the driver selectable Energy Saving modes of "OFF", "NIGHTLY", and "ON" located at "Controls" > "Displays" > "Energy Saving". I believe that the auxiliary 12V battery is still being charged whenever any of these driver-selectable Energy Saving modes are selected, assuming that the main battery is charged above 5%.

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I've always had energy saving turned on (once it was available) and the OE 12V battery lasted almost two years, so I doubt that energy savings is the culprit. Every car with a big battery has 12V battery problems, the Prius, Leaf, and Tesla forums are filled with 12V battery posts. To save 10kg of weight and a bit of cost, every manufacturer puts in the smallest 12V battery they can find, and it doesn't take much to knock it out. Unfortunately, a 12V battery is required because you still want power braking should the main battery be disconnected. It also helps extend the life of the 12V system by stabilizing the voltage. (Tesla did try it without the 12V originally in the early Roadsters, but that turned out to not work so well.)

For the dead battery in 12 days, I suggest (no particular order):

1. Bad luck with a defective battery.

2. The battery sat around for a long time close to fully discharged before being installed.

3. A 12V charging problem with that particular car.

> ICEs put much more strain on 12V batteries with their high initial cranking current. [Barry]

Their batts are designed for that one shot then quick recharge type of service. MS requires deep cycle capability, ie a whole different batt technology.

Unfortunately we will most likely never know the details of this (yet another) 12v batt incident save 'they replaced my 12v batt'. TM keeping all the fun facts to themselves.

4 hour job - yes it is. Try replacing one yourself, not easy (peek in and see). Plus you need to check out the entire DC<>DC system too.
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Barry said:

They told me the service will take 4 hours, so I don't think just showing up at the SC will accomplish anything. They assured me this is an early pre-emptive warning, and there is another message that will appear if failure is near. And for 4 hours of service, they must be doing more than just replacing the battery.

I don't believe it's a primary battery problem. There are just too many reports of them going bad. ICEs put much more strain on 12V batteries with their high initial cranking current. Something else is going on in the electrical system to kill so many of them so soon.

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Tesla could just put a small 11V lithium ion battery into their Teslas and that'll be the end of the discharge cycle problems. Or just put a gel battery in. Cost savings at the wrong end...