If any of you have a MacBook Air, I'd appreciate if you could try the following simple experiment. Fully charge your machine. Close the lid (putting it to sleep). Disconnect the power and go to bed. Eight hours later, open it up and tell me how much juice is left in your battery.

My MBA: 68% left
A friend's MBA: 91% left

Something appears to be funky about the battery drain rate in my machine.

If it turns out that something is fubar with my MBA, what am I supposed to do? Call up the local Apple store and arrange for a replacement? I'm worried they'll want to just replace the battery with another one (presumably, under warranty), when the issue may well be a logic board fault of some kind that's consuming way more power when asleep.

Thoughts?

wireless ?

When it's "asleep", I'd hope that the wireless wouldn't be consuming power. If it is, that's a problem.

Is Bluetooth on? Do you have the pref to allow Bluetooth peripherals to wake the machine on as well?

A good thing to check is to see what the system thinks the battery capacity is on your machine and your friends. To do this, go to the Apple menu, About this Mac. Then click on More Info, and pick the power category on the left side. The info you want is under two sections, and using my MacBook Pro with a new battery as reference, here is what mine says:

Charge Information:
Charge remaining (mAh): 2794
Fully charged: No
Charging: No
Full charge capacity (mAh): 5484

Health Information:
Cycle count: 5
Battery health: Good

Full charge capacity is going to be the key number you want to compare, then also compare charge remaining after your sleep experiment. Verify what Bruno said about Bluetooth settings, and also ensure any USB devices are disconnected to get a good and equal measurement. Make sure the cycle count at least has a few cycles as well, as sometimes it takes a machine a bit to properly calibrate the percentage displays. I've seen my Mac hit 0%, then recalculate and pop up to 15-20% with a new battery the first time through a charge cycle.

Right now, I've got Bluetooth off and that's my default. (I only turn it on if I'm going to be using it for dial-up over my cell phone.) There was nothing plugged into any of the ports while I was doing my battery drain experiment.

With respect to the system info, it currently says my battery has gone through 16 cycles and is in "good" condition.

What about "full charge capacity"? Laptop batteries are smart enough these days it seems to somehow work out a capacity - based on charge/discharge times I assume.

e.g. my 3 year old Dell laptop battery only says about 3800mAh when it's labelled rated capacity is 4700mAh

I called Apple tech support. They had me shut down the machine and do a ctrl-option-shift power button press. This resets the power controller (Apple link). Now I'm charging the machine up again. Once it's charged, I'm supposed to let it fully discharge itself. In theory, this will "train" the machine on its battery.

We'll see.

Update:

Monday, a week ago, I shipped my MBA to Apple. It came back this morning. Same computer, shiny new battery. No other changes, so far as they said on the sheet that came back with it.

I had pre-emptively backed everything up twice (the usual over-the-network Time Machine as well as a Super Duper backup to a USB hard drive), and then I deleted a bunch of personal stuff and sent it in. Interestingly, the computer came back with the hard drive unmolested. Restoring it was an interesting adventure. The Super Duper drive turned out not to be bootable, even though it was supposed to be. Remote booting failed in an interesting way as well. The idea that you're supposed to hold down the option key when you boot. It then dumps you into a dialog where you can select which computer to boot from. Because we've got a big network here, it saw a ton of computers offering Mac boot media. It showed the first few of them and then stopped. There was no way to tell it to go to my specific desktop Mac with its backup. Maybe next time I'll use a cross-over cable.

Anyway, I instead restored my files the "normal" way, through the standard Time Machine user interface. The hardest part was getting Time Machine to recognize its old backup volume (along with a brief panic when it saw an empty backup, for some reason, and was about to overwrite it with something new). Once I sorted all that out, the restore did what appears to have been the right thing.

Tonight, I'll see if the new battery has any less drain when it's "off" than the old battery did...