When handling the battery, avoid squeezing or touching the four exposed lithium polymer cells.

Lift the battery from its edge nearest the logic board and remove it from the upper case.

When installing the new battery, if there is a thin plastic film on your replacement battery, do not attempt to remove it. It is glued on and protects the battery pack while it is inside the MacBook.

If you're installing a new battery, you should calibrate it after installation:

Charge it to 100%, and then keep charging it for at least 2 more hours. Then, unplug and use it normally to drain the battery. When you see the low battery warning, save your work, and keep your laptop on until it goes to sleep due to low battery. Wait at least 5 hours, then charge your laptop uninterrupted to 100%.

If you notice any unusual behavior or problems after installing your new battery, you may need to reset your MacBook's SMC.