1. The screw that holds the bottom cover on is located under the clear plastic handle (photo 1) on the bottom of your iMac. Remove the screw. With one hand, hold the main handle on your iMac, then with the other hand grab the smaller clear plastic handle in front of you (photo 1) and pull it directly towards you to unhook it, then lift the cover up to remove it.
2. With the cover removed you can see the bottom side of the chassis (photo 2). The chassis contains the hard drive, CD-ROM, battery, processor and many other components of you iMac except for the monitor. You need to remove the chassis but first you need to disconnect the four cables (photo 3) that connect the chassis to the monitor and power supply. Loosen the two screws on either side of the main white cable and unplug it. These screws do not come out the only loosen. Unplug the smaller grey cable next to it and remove both cables from under their plastic anchor. Next, remove the small screw on the left hand side (photo 3) which anchors the third cable. Grab the cable by the black plug and pull it up. If it doesn't come out easily, gently try to wiggle it or rock it while pulling it up. NEVER pull on the wires or cables directly always pull on the plug. The last cable (photo 4) is a little different than the others. Grab the plug with two fingers and with a third finger, push down on the front edge of the little tab in the centre of the plug (photo 4) while pulling on the plug to remove it. If it resists, you may need to gently lift up on the opposite side of the little black tab with your fingernail or pen while pulling on the plug. Push the four cables to the sides as much as possible. Next remove the two screws at the top of the chassis (photo 5), be careful not to let the screws fall down the holes. Use your small finger to guide them out.
3. You are now ready to remove the chassis. Notice the plastic handle at the top (photo 6), put your fingers in the handle and slowly pull straight up (photo 6). If it sticks while pulling up, check the cables on both sides to see if they are not preventing the chassis from coming out. The cables stay with the main body of the computer and do not come out. Turn the chassis over and put it down on the table. Photo 7 shows what remains of the main body of the computer. Move this out of the way being careful not to scratch the screen. Photo 8 shows the front side of the chassis when it is fully removed from the computer and the location of the battery.
4. Look down on the top of the chassis and you will see the battery (photos 8). You will also notice that there is a black plastic cover over the battery. You need to pull this cover off. It is just clipped on the sides and comes off quite easily (photo 9). Next, take out the old battery and discard it.
5. Install the new battery. Very important: Make sure when you put the new battery in that it goes in exactly as shown on the bottom of the battery cradle (photo 10). The positive (+) terminal of the battery must match to the positive (+) positive terminal in the battery cradle and same is true for the negative (-) terminal. They must match up.
6. After installing the battery, put the black plastic cover back on over the battery. You are now ready to reassemble your iMac.