Mac Air loses 90% of battery overnight when in Sleep mode

The first thing I suggest is a reset of your Mac’s System Management Controller. The SMC governs how your Mac’s various components are powered and operated. The SMC also deals with putting your Mac to sleep, so if your Mac is not going to sleep properly, an SMC reset can help! Here is a helpful guide that outlines the steps!

Reset the System Management Controller (SMC) on your Mac - Apple Support

The next thing I suggest is that you perform a reset of your Mac’s NVRAM. The NVRAM contains many of the settings that OS X uses to govern how it is run. If there is a setting that has been incorrectly set (basically a software glitch) that is causing the issue, then this should fix it. Here is a helpful guide!

How to reset NVRAM on your Mac - Apple Support

Any of these steps should put your system right at ease.

Cheers!

Hey roperat,

Welcome to Apple Support Communities! I'd check out the "Tips for maximizing your battery charge" article, specifically the following steps which should resolve the issue:

Turn off unused features and technologies
Just as you would turn off the lights in an unoccupied room, turning off unused features and technologies can help maximize your battery life, too. Here are a few suggestions:

• Eject CDs and DVDs you're no longer using. Sometimes the optical drive spins to read CDs or DVDs that are in the drive. This consumes a small amount of power.
• Disconnect peripherals when you're not using them. Connected peripherals—such as printers and digital cameras—can draw power from your battery even when you're not using them.
• Shut down any runaway applications.
• Quit any applications that are running but not in use.

If you're not in a location where you need to use AirPort or Bluetooth, you can turn them off to save power.To turn off AirPort from the menu bar:

1. From the menu bar, click the AirPort icon .
2. From the drop-down menu, choose Turn AirPort Off.

To turn off Bluetooth from the menu bar:

1. From the menu bar, click the Bluetooth icon .
2. From the drop-down menu, choose Turn Bluetooth Off.

You can also turn off Bluetooth or Airport from System Preferences:

1. From the Apple () menu, choose System Preferences.
2. From the View menu, choose Bluetooth or Network to open the appropriate System Preference pane.

Mac notebooks: Tips for maximizing your battery charge

http://support.apple.com/kb/ht1446

All the best,

David

Modern systems that support PowerNap (the Air being one) will wake up for various tasks, including backing up and software updates, so some of these might be the cause (see here: http://support.apple.com/kb/ht5394).

The issue could be fixed by an SMC reset if the power nap feature is being improperly handled, or at least tested by unchecking the "Enable Power Nap" option in the Energy Saver system preferences.

Give those a shot, to see if they at least show a difference. See here for how to reset the SMC for your system: http://support.apple.com/kb/ht3964

You don't mentionn whether you have any peripheral's plugged into the computer. If you do you might want to unplug them before you shut the lid to put the computer to sleep. Unplugging a USB device after the computer is asleep generally wakes it and sometimes it won't go back to sleep.

When you shut the computer's lid the console should record a sleep command and similarly when you lift the lid it should record a wake commend. Open the console and do a search on 'wake'. You should see a reference to Wake - reason LidOpen at the time you lifted the lid. If you aren't seeing that it means the computer isn't going to sleep when you close the lid.

Resetting the SMC often fixes this issue but failing to sleep can also be software related so if doing an SMC reset doesn't fix it let us know and we can start looking for software issues.