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Battery experts opinion regarding traction battery life

If you take two identical long range Model 3 traction batteries and performed the following test what effect would it have on longevity?

Both batteries would be in a temperature environment that did not vary below 60F or above 80F.

One battery would be charged to 80% and stored on a shelf for a year or have the 12V battery removed from the car (very close approximation to the same thing). Actually Tesla recommends disconnecting the 12V for long term storage if AC charging power is not available. Quote for a Tesla Service document - "Storing the vehicle for three weeks or more (unless it is plugged in)"

The other battery would be in a plugged in Model 3 not driven for a year but the charge level would be set and maintained to 80%.

At the end of the year approximately how much life span would be lost in both scenarios given the following assumptions?

Phantom drain is supposed to be around 1% per day or about 3+ miles; however, over the ownership of the car I have seen up to 20 miles of drain in a given day.

I will use 4 miles average for the following observations:
4 miles X 365 days = 1460 miles of Phantom drain in a year
It is my understanding the charger will charge the battery back to 80% when it has lost about 10 miles/3% of the 310 mile range.
1460 miles / 10 miles is approx 146 3% charge cycles on the traction battery (and an equal number to the 12V battery) in a year.

I know hardly anyone would ever not drive their car for a full year (maybe it would apply to someone serving in the military) but I am still curious what the difference would be to the traction battery longevity.
Nobody knows, and if storing I would set to 50%.

When you saw 20miles of phantom drain I suspect that was cabin overtemp protection not phantom drain.

What I can tell you is my 2014 P85 that started life in New Mexico and has now endured into the low 20s BELOW ZERO with 86k miles on it seems to be 6.5% degraded. Traction pack is the least of my concerns.
Twice in the 21k miles I have owned it it has been disabled by relatively small problems and currently has several problem I have to take it out of state to get resolved. I love the car but the car around the battery and motor are not going to last long enough to worry about the pack or the mythical half million miles from the electric motor.


Well-Known Member
Apr 13, 2018
Buford, GA
You are asking for a comparison between what you suggest are identical situations and then asking about phantom draw, and seemingly trying to correlate the two.

My answer? Don't worry about it.

Just use the car, enjoy the car, stop worrying about the batter, let the car make you happy. If you keep the car for the length of the battery warranty, I think that you'll end up being happy.
Actually the 12V battery could be cycled up to 2.5 times more than the traction battery depending on how many times the car wakes up due to the need to top off the 12V battery. Maybe/probably the 12V battery is always topped off anytime the car is NOT sleeping even though the lower voltage threshold has not been reached? I am not real concerned about the 12V battery longevity due to charge/discharge cycles because is fairly inexpensive maybe around $250? However, 12V cycling has to reduce its life as well.

I know just drive the car and be happy but many engineers and scientists brains don't work like that (they are curious how things work).
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