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We had a snow/ice storm last night, and somehow the snow got into the engine area. Is it possible that the snow covering the battery was the case of draining the battery?

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    \$\begingroup\$ Possible of course but highly unlikely. If the battery is old or otherwise gone bad, it can fail to start the car when it is cold. \$\endgroup\$ – Justme Dec 24 '20 at 23:25
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    \$\begingroup\$ I’m voting to close this question because it's not an electronics design question. It's more suitable for one of the auto (mechanics?) SE sites. \$\endgroup\$ – Transistor Dec 24 '20 at 23:35
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    \$\begingroup\$ If there's an electrolyte, such as typical car battery goo, or dried salt spray from the roads you live in northern states, then the melted snow can make a pool of salty liquid . . . . \$\endgroup\$ – Pete W Dec 25 '20 at 0:53
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    \$\begingroup\$ unless it was -30’C I would assume from 50+ yrs living in Winterpeg, that snow was not the cause/fault of your battery. I can think of a dozen other reasons. \$\endgroup\$ – Tony Stewart EE75 Dec 25 '20 at 8:10
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    \$\begingroup\$ @acoder what's the date printed on your car battery? If its older than ~3 years the common advice is simply "replace" and ideally with the biggest one that will fit in the space, with the same terminal config/size/orientation. Newer cars simply go through them faster, whereas older cars seem to get more life out of their starter batteries. \$\endgroup\$ – Criggie Dec 26 '20 at 13:18
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As in here

https://www.cambridge.org/core/journals/journal-of-glaciology/article/engineering-properties-of-snow/640B715A5752FE7DFD2C6EA2391AC00C

Reported values of d.c. conductivity for snow vary considerably, partly because there really is wide variation, and partly because there are measurement problems.

“cold” snow of unspecified density; in these studies, d.c. conductivity stayed within a surprisingly narrow range, from 9×10⁻⁷ to 4×10⁻⁶ Ω⁻¹ m⁻¹

and

conductivity increases by three orders of magnitude as temperature increases from —60 to — 10°C, and there is a sharper increase at temperatures above —10°C. The Tsuda, 1951 data (Fig. 28) show the rapid increase in conductivity that occurs as free-water content increases in “warm” snow.

D.C. conductivity as a function of temperature, with density as parameter. (After Kopp, 1962.)

To answer your question,

Is it possible that the snow covering the battery was the case of draining the battery?

It is possible but unlikely. The resistance of snow per meter, even when at close to 0 Celsius, is in the order of Mega ohms, unlikely to cause a more significant effect than the standby power consumption of automobile electronics and the self discharge of the battery. According to here https://shop.advanceautoparts.com/r/advice/car-technology/why-do-car-batteries-fail-in-winter

But as the chemical reaction occurs, the positive and negative lead plates are slowly coated with lead sulfate. This process is known as sulfation, and it reduces your battery's ability to hold a full charge.

freezing temperatures slow the chemical reactions occurring inside a lead acid battery, further reducing your battery's ability to perform.

It is more likely the temperature extremes exposed the problems on an already failing battery.

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    \$\begingroup\$ Thanks for the answer @johndoe because the question was about workload of snow draining a battery, not about mechanics of a motor and battery. I highly doubt a mechanic would know the answer, but an EE such as yourself would :D \$\endgroup\$ – a coder Dec 25 '20 at 3:22
  • \$\begingroup\$ In addition, note that the heat from the battery discharging into the snow would likely pretty quickly melt the snow. More likely, as you say, the cold caused the failure. \$\endgroup\$ – SomeoneSomewhereSupportsMonica Dec 27 '20 at 1:34
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Water with impurities is a good conductor,  but snow is pure H2O, with a stable bond, and a poor conductor of electricity.  Factor in your positive terminal covered by a plastic cover with a plastic battery case.  So anything is possible, but not likely.

I live in a region with high winds and snow fall to hide cars in drafts or snowfall.  Getting snow under the hood is a common occurrence.  Never had a problem with dead batteries or starting car. 

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  • \$\begingroup\$ Snowflakes usually nucleate onto an impurity, but I agree that the formation of snow is, in general, more pure than, say, tap water. Also, snow catches impurities as it falls through the sky, just like rain: thoughtco.com/is-it-safe-to-eat-snow-609430 \$\endgroup\$ – Lawnmower Man Dec 25 '20 at 21:58
  • \$\begingroup\$ Certainly, but the core or edges may not be pure, but majority is pure water. \$\endgroup\$ – StainlessSteelRat Dec 25 '20 at 22:07
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Possible? Yes, assuming that the surface of the battery was not completely clean and some of the snow melted.

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  • \$\begingroup\$ As a chemist I think this is the best answer for why a battery might actually discharge. A battery in a car is likely to have all sorts of grim on it that would dissolve in melted snow. \$\endgroup\$ – MaxW Dec 25 '20 at 17:26
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Like John Doe answered, snow on top of the battery is unlikely to cause a significant drain, because the distance between + and - terminals is so large. Temperature sounds like a more likely explanation in this case. But for future reference, I'll add a bit more details of signs of water getting into electric circuits below.

Distance and resistance:

If water and especially if water and salt got inside some connector or circuit board where the distance between + and - conductors is only a few millimeters, there could be significant drain. Snow is slightly conductive, but if the surfaces are even slightly warm it would melt into water and conduct quite well. Because the distance is smaller, the resistance is smaller and the current flow is much larger. This would however also cause visible damage to the conductors.

Electrolysis:

Electricity flowing through water causes electrolysis, where metal atoms from the positive conductor transfer to the liquid and from the liquid to the negative conductor. This causes fast corrosion of the positive conductor and creates blue or green copper oxides.

The amount of electricity in a typical car battery is around 100 Ah. In electrolysis, this would transfer 100 Ah / qe / Na = 3.7 mol of atoms. For copper that is 240 grams in ideal conditions. Even with practical losses, discharging a fully charged car battery through electrolysis would be enough to completely disintegrate the conductors, requiring replacement.

Practical considerations:

Usually it happens that the water evaporates due to the generated heat and the electrolysis stops before the battery is empty. Sometimes the deposited metal on the negative terminal creates a direct metal short-circuit, which could fully drain the battery or even cause a fire.

Of course well manufactured automotive electronics are protected against water ingress where insulation distances are small, so for this to happen the seals would have to be already broken.

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