I drove a honda civic hybrid in Northern Ontario for two winter seasons. The batteries where NiMh and the cold was absolutely brutal on them. Indeed they'd recover a bit of charge when warmed up but it was usually very hard to tell if that was because of the engine running or because the batteries warmed up. (and sometimes even harder to tell because the displays wouldn't work at all below -25 celsius).

Maybe the batteries Tesla uses recover better/faster but since it's all electric there is obviously no way to get more power into the pack so the only thing that using a heater will do is drain it, and it will drain it pdq. If I was driving an all electric car and I was worried about my range the one thing you can be sure of is that I would maintain as constant a speed as possible and the heat would be off. After all it is a lot better to arrive at your destination cold than it is to deplete you battery and spending even more time in the cold.

I'm pretty sure Tesla knows the exact power curves for their batteries at any temperature condition that could realistically speaking occur, if they were asleep at the switch that's a big bad problem for them but if they had this info and used it and this is turning into a game of words rather than a game of data then the only thing they should do at this stage is to have a Tesla engineer duplicate the trip conditions to see what the result would be if you behaved rationally rather than irrationally.

That way we'd get some usable information. Experiments are only valid when you can repeat them.

Are Tesla's customers all Tesla engineers? If not reproducing the run with a Tesla engineer is pointless.

How is having an engineer reproduce a failure condition under controlled circumstances pointless? That's how bugs are fixed.

This is not my area of expertise at all, but that sounds backwards.

As I understand it a given number of molecules' bonds can be broken at any point to generate current. In colder ambient temperature the propensity to generate current decreases. However, the quantity does not. In other words, the apparatus for measuring what "charge" is available will incorrectly judge how much is left, but an intelligent system on the other hand may also take into account what the ambient temperature is doing to the sensor of how much current flows given a certain test circuit.

I'd guess that there is not an objective way to measure the charge left. I'd also guess that at a colder temperature it might not have as much power or as much torque, but that it would not affect the range, especially if the battery if artificially (or intrinsically) warmed once it gets toward the "bottom" of its capacity.

What the support people could have been talking about is how to game the system so that the sensors report a more reasonable gauge of the true range. That means that the supposed decrease overnight was not that the potential energy dissipated, but that the colder temperature lead to less accurate readings. Causing a current draw through driving slowly in the parking lot and running the heater might cause the battery to heat up, and thereby affect the current available to a test circuit, something that matters to the sensors' test circuits.

I'd like to hear from someone who actually knows something about electrical engineering, but without being informed on the field, it looks like a failure of imagination in assuming good faith and imaging possible scenarios.

gratuitous analogy:

Let's say it is a fictitious 1975 where Porsche has remote telemetry, and a NYT reviewer is skeptical about oil-cooled engines, because he states that you may run a little low on oil then also be low on coolant or vice versa. In the early morning of a freezing day, he looks at the dipstick. It says he is a three or four quarts low! He calls support, and they tell him that he will have more oil if he warms up the engine, and he'll be able to go for a drive without hurting the engine. (They should have said that he would get a more accurate measurement rather than get more oil) So, he starts the car, revs the engine, drives in circles, etc. Maybe he checks the oil again, maybe not. He takes off, and a couple hours later the engine seizes up. Apparently, it was both looking like it was extremely low on oil and was also actually very low on oil. The telemetry shows the reviewer appearing foolish, and possibly trying to ruin the engine. You could say that he is a professional and should have been able to parse the statements from support more intelligently. Yet they both look bad, but it may not be an inaccurate depiction of what end users would experience.

I was speaking informally earlier, but if we make things more precise then I think we're pretty much on the same page.

I think you're right when you say:

>In colder ambient temperature the propensity to generate current decreases. However, the quantity does not.

Presumably, the car stops running when the battery's propensity to generate current ("voltage") falls below a certain threshold. If that propensity to generate current does decrease when it's cold, then a cold battery will hit that car-stopping threshold earlier, right? Assuming the battery stays cold.

That's all I meant when I said "a cold battery has a shorter range".

And when the battery warms up, its chemical reactions speed up, increasing the voltage and pushing the car-stop threshold into the future. That's what I meant by "As the battery warms up, the estimated range should go up as well."

The battery's "state of charge" in the plot from Musk's blog post does go down overnight. Whether that's due to self-discharge, some system in the car that used a bit of energy overnight, or some temperature-related measurement effect (or a combination of those things), I don't know. I just thought it was striking that the "estimated range" dropped so much more than the "state of charge" (at the 400 mile mark in Musk's plots).

Does that put us on the same page?