I have the same Air as you and I am getting 5-6 hours. So not to much off of what the advertised amount is. Your battery sounds faulty to me.
The last computer I had had a faulty battery. It was replaced for free and within a couple of days. Back then they simply replaced the battery on the MB because it was removable. Chances are now they will give you a new laptop because the battery on the Air is harder to remove. You might be without a computer for a few days though. I don't know what they do in other countries, but in Spain they just took it and mailed it to Holland to get fixed and then mailed it back.
The autopoweroff feature is also mentioned in http://support.apple.com/kb/HT1757:
With the release of the OS X Mountain Lion v10.8.2 supplemental update 2.0, a new feature was introduced to enter safe sleep after four hours of the computer being connected to AC power. This is an effort to comply with the European Energy Standards (ErP Lot6). This will only occur if there is no wireless or Ethernet activity and no activity from external devices such as USB storage devices.
This is normal behavior for the following models:
- MacBook Pro (Mid 2012 and later)
- MacBook Pro (Retina, Mid 2012 and later)
- MacBook Air (Mid 2012 and later)
- iMac (Late 2012 and later)
- Mac mini (Late 2012 and later)
Standby mode is documented in http://support.apple.com/kb/ht4392:
Macs that can use standby mode:
- MacBook Pro (Retina, 13-inch, Late 2012) and later
- MacBook Pro (Retina, 15-inch, Early 2013) and later
- MacBook Pro (Retina, Mid 2012)
- MacBook Air (Mid 2010) and later
- SSD and Fusion drive versions of Mac mini (Late 2012) and later
- SSD and Fusion drive versions of iMac (Late 2012) and later
Mac computers manufactured in 2013 or later enter standby after three hours of "regular" sleep. Earlier computers activate after just over an hour of "regular" sleep.
To enter standby, the computer must:
- Be running on battery power (if it is a Mac notebook computer).
- Have no USB devices attached.
- Have no Thunderbolt devices attached.
- Have no SD card inserted.
- Have no external display attached.
- A computer with a fully charged battery can remain in standby for up to thirty days without being plugged in to an AC power source.
The state of the computer is saved to the flash storage (SSD), then the power to the hardware subsystems turns off to increase the length of the standby. For example, RAM memory and the USB bus are powered off during the standby.
So standby mode and autopoweroff are supported by different models of Macs and they are enabled under different conditions. Standby mode was introduced in 2010 and it was initially only supported by MacBook Airs, but it is now supported by all new Macs except Mac Pros, iMacs with no SSD, and Mac minis with no SSD. autopoweroff was introduced in 2012 and it is supported by all new Macs except Mac Pros.
I don't know if the state of being in standby mode is different from the autopoweroff state. A gray screen with a progress bar is shown when a Mac wakes up from both states.
Note that Apple has used "safe sleep" to refer to both the hybrid sleep and hibernation mode that laptops use by default (like in http://support.apple.com/kb/PH11096) and to the hibernation-only state (like in the first block quote above).
Even if you set standbymode to 0 and disable standby mode and autopoweroff, you won't waste that much energy. New laptops use about 0.7-1W of energy in sleep mode and about 0.2-0.3W when off or in hibernation mode.
Best Answer
I had a similar problm, and found that there was no ready-made solution to force the computer to sleep at a different battery percentage (eg. go into "Safe Sleep" at 5% instead of 1%).
The (lame) workaround I ended up using was using SlimBattery Monitor to issue a pop-up warning at a custom battery percentage (for me it was 20%), at which point I must close my laptop/manually tell it to sleep, until I can get it on AC power.
It seems you would have to write your own applescript to make the computer sleep if the battery is too low, and add a LaunchAgent to have it repeatedly run the script to check the battery power. Annoying enough that I didn't venture down that path. I was surprised none of the many battery-monitoring programs had this funcitonality (I may have just missed the one that does).