If this was a current-model Mac laptop, these upgrades would be impossible, since current models have glued the battery to the case and soldered the SSD to the motherboard, but Apple has not (yet) made these anti-repair changes to the MacBook Air series.
To upgrade the computer, I bought a 480G SSD upgrade kit and a replacement battery for it. Total cost was approximately $380. The kits include the special screwdrivers needed for installation and a USB enclosure for the old SSD (more on that later).
The first step before starting any major job like this is to make a full backup of the system. It's actually a good idea to make two full backups, just in case one fails, since you really don't want to have to explain why everything got trashed, should the upgrade go wrong. I had already purchased two external hard drives for my daughter to use in college (a 2TB portable drive and a 4TB desktop drive), so I used them to hold bootable full-system backups. After using Apple's Disk Utility to re-partition the drives for a GUID partition table and format each with the Mac OS Extended file system, I used Carbon Copy Cloner to copy the system's recovery partition to the external drives and make a full bootable backup of the system. After test-booting the computer from each of the backups (hold down the Option key while booting, then select the USB drive to boot from it), I was all set to upgrade the computer.
I don't have photos of the procedure (didn't think about it until I started writing this article), but if you require detailed instructions, iFixit has detailed repair guides for most Mac computers. For a 2011 11" MacBook Air, they have repair guides for both the battery and the SSD.
The procedure I followed to do both upgrades at once was:
- Whenever working inside of a computer, be careful about static electricity. Wear an ESD wrist strap if you have one. If you don't and you don't want to get one, work on a smooth (non-carpeted) surface and touch grounded metal (like a steel lamp or table leg) often while you are working. And never touch exposed circuitry on anything you handle while working.
- Remove the 10 screws from the back of the case. This requires a special pentalobe screwdriver. The upgrade kits I purchased include this screwdriver. When removing them, note that there are two long screws and eight small ones. Be careful to not mix them up later on when reassembling the computer.
- With the screws removed, the back case comes right off. Set it aside so it doesn't get damaged when you need it later.
- Locate the connector that attaches the battery to the motherboard. You can disconnect it with your fingers, but you will find it much easier if you use a plastic spudger Do not use any metal tools - they can damage the plastic connector. Do not use force - the connector should come off without much effort. If it seems too tight, look more closely. You want to disconnect the battery's connector from the motherboard's connector. You do not want to pry the motherboard's connector from the motherboard - if you do that, you will cause permanent damage and will probably have to buy a new computer.
- With the battery disconnected, remove the five Torx screws that hold it in place. The upgrade kit I bought included the screwdrivers. Please note that these screws come in three different lengths. Be careful to not mix them up.
- Remove the old battery and set it aside.
- Locate the SSD. It is held in place by one Torx screw. Remove it and set it aside. Slide the SSD from its socket by sliding it horizontally. You can lift it a little, but try not to - you don't want to accidentally damage the socket.
- If you bought an enclosure for the old SSD, now is a good time to install it. (See sidebar)
- Install the new SSD. Taking care to avoid ESD damage, remove it from its packaging. Gently press it into its socket until it is firmly seated. If it doesn't fit easily, note the orientation of the connector. It is not symmetric and will not fit if the SSD is upside-down. Once the SSD is seated, secure it using the Torx screw you set aside when removing the old SSD
- Place the new battery in the computer. It is on a plastic frame that will align with the five screw-holes in the case. Make sure its connector is over the motherboard's battery connector. If it isn't, then you have the battery upside-down. Secure it to the case with the five Torx screws you set aside when removing the original battery. Be careful to use the correct screws - there are three different sizes and you will cause damage if you put them in the wrong place. Do not over-tighten the screws or you can strip the aluminum base.
- Snap the battery's connector to the motherboard's battery connector. Look closely to make sure all the pins align correctly and then press firmly until you hear it snap into place.
- Put the cover back on the computer and secure it with the ten pentalobe screws you removed when opening the computer. Be careful to use the correct screws - there are two different sizes and you will cause damage if you put them in the wrong place. Do not over-tighten the screws or you can strip the aluminum base
To copy everything to the new SSD, boot from one of the backups. I used the old SSD (mounted in its USB enclosure) because it is much faster than the hard drives I used for backups. Attach the backup drive, hold the Option key while booting and select the external drive to boot from it. The boot sequence will take longer than you're used to - this is inevitable because USB 2.0 (what the Mac Book Air has) is much slower than the internal SSD interface and hard drives (if you booted from a hard drive backup) are much slower than SSDs
When the system has booted (from the external drive), use Disk Utility to partition and format the new SSD. As with the backup drives, use a GUID partition table and format the partition using Mac OS Extended format.
Now, clone the external drive to the internal one. Use the same software used when making the backup. Using Carbon Copy Cloner, I first copied the recovery partition to the new SSD, then cloned everything else to the main partition.
Once everything has been successfully cloned, shutdown the computer, disconnect the USB drive, and boot from the (new) internal SSD. It should just work at this point. After booting, go to the Startup Disk system preference to select the internal SSD, because the old value will be invalid (pointing to the no-longer-present SSD), causing the system to boot more slowly than necessary.
And now it's time to upgrade the software. This part actually made me more nervous than the hardware replacement because I was going to be jumping forward five macOS releases, going from 10.7 ("Lion") to 10.12 ("Sierra" - the current version). Fortunately, everything went smoothly. Launch the App Store and click on the Upgrade tab. There is a giant ad at the top of the window requesting an upgrade to Sierra, including an "Upgrade" button. Click it.
At this point, the Sierra installer downloads (about 5GB, which took about 35 minutes to download over a 25Mbps cable modem). Once downloaded, the installer starts to run. It will ask you to click a button to begin installation and then ask for an administrator password. Provide this information. The system will reboot and installation will continue. It will take a while (over an hour), but you can't just ignore it, because there are two or three times where you will have to click a button to continue. When finished, the system will boot up to a Sierra login screen (or the account you have configured for auto-login, if you have configured that). When you log in, you will be asked for your Apple ID and password for setting up iCloud, and if you want to set up Siri. You can skip both steps, if you wish. Please note that every user on the computer will be presented the same setup windows the first time he logs in after the upgrade.
But you're not quite done yet. Go back to the App Store's Updates tab and look for more updates. In my case, there were several. There were two application updates (iPhoto and iMovie), a Thunderbolt firmware update, and updates for iTunes and updates for printer drivers. You may have to reboot as a part of some of these installations. Repeat this process until no more updates are available. (For some reason, the Thunderbolt firmware update needed to be installed twice before the App Store stopped asking me to upgrade it.)
With macOS fully upgraded, the next step is to update applications. I used the auto-update features of Firefox and Chrome to bring them to the current versions. I had to repeat the process multiple times for Firefox - it won't jump all the way from version 22 to 55.0.2.
Finally, I updated Microsoft Office. After launching an Office application (I used Word, but any one will do), I was asked to re-authorize the installation. I assume this is because the new SSD causes its hardware ID to change. Fortunately, I retained by license key from the original installation. I typed in the key, Office accepted it, and the applications launched properly. I then used the Microsoft auto-update tool (select "Check For Updates" from the Help menu) to download and install all available updates, repeating as necessary until there are no more updates to install.
And software installation is done. The only remaining task is to calibrate the new battery. Although Apple doesn't consider this necessary for modern Macs, the battery's manufacturer explicitly requests (as a part of its installation instructions) that this be done, so I did. I followed the link included with the battery and followed the documented procedure.
And now it's all good to go. My daughter's computer now has four time its original storage and a brand new battery and is all ready for use when she goes off to college next week.