MacOS – Model Name: MacBook Air Model Identifier: MacBookAir4,2 Processor Name: Intel Core i7 Processor Speed: 1.8 GHz

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.

Open a support ticket with AppleCare if you'd like expert help in determining whether they can run diagnostics remotely to measure a few more data points than the overall summary.

It could be a high GPU / CPU / firmware thing that needs updating, but it also could be a battery that soon enough will show less life than designed and you'll be offered an exchange under warranty.

You can also open terminal and issue a few commands to look in more detail at power management.

 pmset -g rawlog

 pmset -g pslog

If you record the settings you have, correlate things with date; io_stat 300 you should get a good indication if the estimates are off and why. Of course, start with the machine 80% charged or more and let them run as your battery drains. AppleCare might not need all the logs, but you can send them / save them and run a check in 3 or 6 months to see if the battery is substantially worse / same / better than now.