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I know that keeping the battery of a MacBook Air in a hot environment is a bad idea. But sometimes I have to leave it in a hot car. Are there any recommendations as to what to do in this kind of scenario?

I'll usually close the lid, which puts it into sleep mode, but I just realized that the battery is probably still being used in that case; and using a battery while it's hot is worse than storing the battery in a hot environment. Is this right? And would the recommendation then be to shut off the computer? What other things are recommended?


According to Apple's webpage:

Hot Tip
If you use your iPod, iPhone, iPad, or notebook in temperatures higher than 95° F (or 35° C), you may permanently damage your battery’s capacity. That is, your battery won’t power your device as long on any given charge. You may damage it even more if you charge the device in these temperatures. Even storing a battery in a hot environment can damage it irreversibly.

Notice the relationship for bad things to do with a hot battery:

Storing < Using < Charging

In other words, the worst thing to do is to charge the device at a hot temperature. Then comes using it, followed by storing it (i.e. storing the battery is the least damaging thing you can do).

So the question is when the device is sleeping in a hot car, is the battery usage (i.e. to keep the RAM data) significant enough that I should be shutting down the computer rather than sleeping it?

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3 Answers

Putting a computer in a hot car is a bad idea. The additional heat, generated by a sleeping MacBook is almost zero.

If you have to leave your computer in the car, and temperatures are (or will reach) near the storage limits (45°C/113°F) you should leave it in an thicker or insulated bag, that will protect the computer from the heat. Avoid direct sunlight at all cost.

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I'm not concerned about extra heat by the sleeping MacBook. I'm concerned that it may be drawing power from the battery while it's asleep (e.g. to keep the RAM data alive). And drawing power from a hot battery is a lot worse for the battery, than storing the battery at the same temperature while the computer is off. –  Senseful May 13 '12 at 17:27
    
I updated the question with proof from Apple's website. –  Senseful May 13 '12 at 17:36
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I believe that everything converges to generated and dispersed heat and think it's safe to assume that a sleeping computer is not a working computer. –  mspasov May 14 '12 at 9:20
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According to the tech specs, you should not store your MacBook Air in temperatures over 45° C or 113° F. While we can assume Apple's specs are a bit conservative (better safe than sorry), doing so might risk damaging your computer, or reducing its lifetime. Note that temperatures inside a car in the sun on a hot day may rise well above 60° C / 140° F.

Being in sleep mode vs. being completely shut down would not make any significant difference, as the battery discharge is neglectible, and while in sleep mode no considerable additional heat is produced by the computer.

The only proper advice I can give you is not leaving your computer in a hot car.

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Are you sure that the negligible discharge doesn't significantly alter the battery's lifetime? Can you link to a website/expert that talks about it? And what if I leave it in there for many hours such that at any given moment it's not discharging a lot, but taken as a whole, it does discharge a significant amount? –  Senseful May 13 '12 at 17:40
    
Seems like you cited your source yourself in your updated question :) A sleeping computer is not one being used. –  Gerry May 14 '12 at 13:01
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When your machine is sleeping, it is still discharging the battery, albeit much more slowly. In this state, the system state is still in RAM, and that means power from the battery is being used to maintain it in RAM. On Windows, it is possible to "hibernate," which stores system state to disk and fully powers down, thus virtually eliminating battery discharge. On Mac OS, you can change to a Sleep mode to simulate "hibernation" such that your system state is written to disk and no power is used to maintain state in RAM; see this thread over on Super User.

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The question is if this slow usage of the battery while it's in sleep is significant enough that it is damaging the battery more quickly than just storing it in the hot car. –  Senseful May 13 '12 at 17:37
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