HI, I am an ex mac genius who was a genius at apple for 5 years. Please add the following tip to the above and any mac where the battery has no hard casing. The first thing we had to do was to add a plastic shield over the battery as it is not shielded at all. Any puncture of that battery by a screw or screw driver will cause and explosion of the battery. So please take care to install a plastic shield before working on the mac. Take the back off, install the shield. At apple we had specific shields that fit the batteries exactly. Try to get these or at the very least tape a protective plastic sheild that covers the entire battery before working. If it does explode we had a safe with a bag and some sort of solution in it. Be careful with all macs that have an exposed style battery. They did this to make the computers thinner, but the shield that was removed to make this happen, must be replaced when working on the machines. Thank you.