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I often put my laptop to sleep at the end of the day with 20%+ battery remaining. When I open it the next morning, it complains that it's at dangerously low battery; it seems to have used up 10% or more just sleeping for eight hours.

The laptop is less than a year old. What's going on here? Is it waking in the middle of the night and ordering itself goodies off Aamzon? Does it have COPD?

My old Windows machine would wake/sleep repeatedly through the night, attempting and failing to hibernate...but I've never heard of a Mac doing that.

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Sleep reduces, but it does not eliminate, battery consumption. You have to keep the RAM chips alive, some processing is done, the hard drive may spin up for various cron jobs.

Hibernation (saving RAM to disk and powering off) and shutting down are the only true ways to eliminate battery usage.

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MacBooks don't spin up to process cron jobs or for any other reason when they are asleep. – JDB Oct 20 '10 at 18:41
Another thing could be that it's not sleeping right away because it's processing. But ~10% battery life over 8-10 hrs is not uncommon. @JDB: I'm not sure about that, I remember mine would wake up periodically, spin for about five minutes, and then return to sleep. – Josh K Oct 20 '10 at 20:37
This isn't normal behavior. Did you have external peripherals attached or was the screen not shut? I've read a few articles about resetting the system management controller to fix this. – JDB Oct 21 '10 at 19:03
@JDB: I mean a ~10% loss of battery life. If you sleep it at ~20% I would expect to wake up with it around ~10%. – Josh K Oct 22 '10 at 13:34
I bet the behavior you're talking about is from having 'Wake on Network Activity' selected in your energy saver preferences. Alternately, you might have a faulty lid sensor (common in non-unibody Macbook Pros). – coreyward Oct 22 '10 at 23:21

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