It was time to replace the battery in my 13" Macbook Air.

How did I know it needed replacement? My computer was taking an inordinate amount of time to charge. It frequently shut down sporadically. When I unplugged the charger the display dimmed. I clicked the "Apple Logo", chose "System Report", then clicked "Power "and it showed that the battery had had over 500 cycles. I made certain the computer was updated to the most recent operating system. I then deleted all unused Apps and ran a diagnostic program to make sure there was no malware. I left the computer connected to the charger for a week and had no shutdowns so I was pretty sure the battery was the culprit

Supplies

Make certain you order the correct battery. To ascertain this, click the "Apple" logo then click "About this Mac"

The manufacture date will be displayed. In my case it was early 2015.

You will need this info to order the correct battery. I got mine online for about $70 CDN. It came with extra screws, a P5 Pentalobe screwdriver and a T5 Torx screwdriver which are necessary for disassembly and re-assembly. I used the empty box to draw a diagram of the computer bottom with the screw locations circled and a diagram of the battery with the screw locations circled. Don't try to use any other screwdriver. The parts are tiny and delicate. Buy the right stuff.

Step 1: Open It Up

Completely shut down the computer.

Flip it upside down with the logo at the top. Use the pentalobe screwdriver to remove the 10 screws one at a time and place them on the corresponding circle on the diagram. Important: as 2 screws are longer and must go back in the same location. Get your fingernails under the cover, lift it off and place it aside.

Step 2: Disconnect the Battery

Disconnect the battery.

Grab the handy plastic pull tab and pull it toward you. Do not pull up!

Use the torx screwdriver to remove the 5 screws holding the battery in place. Put them in the correct circle on your diagram. Important: 2 screws are longer and must go back in the same locations.

Step 3: Remove the Battery

Carefully pry up the front edge of the battery using only fingers.

It should lift right out. Don't bend, flex or squeeze it. Dispose of it at a proper recycling facility.

Step 4: Install the New Battery and Re-assemble

Gently place the new battery in position but you will have to plug in the connector first!

Then position the battery correctly. Replace the torx screws in the correct positions.

Replace the cover making certain the pentalobe screws are in the correct positions.

Power up your computer. It should work as before.

Click the "Apple" logo, click "System Report," scroll down to "Power." The computer should recognize your battery by displaying the manufacturer's name and show that it is in its first cycle. If so, you are good to go.

Follow the battery manufacturer's recommendations for charging, etc.

This is not a difficult project. It took me about a half hour. I do suggest buying the correct tools and using only gentle finger pressure on all parts. Resist the urge to use pliers or any kind of prying tools. Also, if you drop any screws into the works, be certain you retrieve them before you re-assemble.