@matigo iFixit.com is the answer, for example, here's the instructions for swapping out the battery in this 2014 MacBook Air 11-inch: https://www.ifixit.com/Guide/MacBook+Air+11-Inch+Early+2014+Battery+Replacement/24735 Very straightforward.
// @skematica
@variablepulserate 2011 is quad-core MacBook Pro with dedicated graphics card & 12 GB of RAM. 2014 is dual-core, lower-clocked MacBook Air with 8 GB of RAM & integrated graphics.
// @matigo
Seems I may have tracked down the former user of this ex-Apple MBA: She's an Enterprise Business Development Manager in Sydney, Australia. Her name was on a sticker on the base of the computer and it was showing as paired to her Magic Mouse.
Fired up the old MBA under Recovery drive & erased the SSD, then downloaded a new version of El Crapitan to do clean install on it. Took about four hours all up. Only one update required, that being RAW camera compatibility.
Brake fluid is a subtle chemical to attack other vehicles' paintwork, it softens the paint slowly & insidiously. PVC conduit cement is far more violent. In 30 minutes it can bubble a painted surface back to the base metal.
// @matigo
Now I need a 2 TB ext HD for Time Machine backups of this 512 GB MBA. I used to use a 650 GB partition of a 750 GB HD for Time Machine with the 128 GB MBA & used the remaining 100 GB as a clone of the system. I'll set up 1.7 GB for Time Machine & 300 GB for a clone. I reformatted the 750 Gb ext drive into a single volume to use as a temp Time Machine backup until I can get an ext drive. An office supplier has WD 2 TB drives for $109 but I hate the extra WD partition you can't get rid of. So I'll possibly get a Seagate or Toshiba drive for about $20 more.
And yes, I did key the old trollop's car door. If you can't get out of a car without causing damage to vehicles already parked then you deserve all the shit you get.
Reminds me of a time some 30 years ago when I returned to my car to find a bastard had angle-parked within 5 inches of mine. I was driving a Ford Escort window van at the time, 
very like the one in the attached pic, but white & without the fancy trim. The exterior door handles protruded & were quite solid.
I climbed in via the rear cargo doors, wriggled into place behind the steering wheel and opened the driver's side door. Violently. Into the offending vehicle's passenger door, leaving a shallow dent. It wasn't a shallow dent when I left the scene, as I'd repeated the door handle application twice more, with equal force. Fixed that bugger.
The faster read/write speeds are for the 2014 MBA vs the 2011 MBP.