HOW TO REPLACE YOUR LAPTOP BATTERY
If your laptop battery fails or no longer holds a sufficient charge, you can easily replace it. Follow these steps:
1. Turn off your laptop and disconnect the AC adapter.
2. Release the latch or other attachment devices that hold your battery in place.
3. Slide the old battery out of its compartment or storage bay.
Avoid touching the contacts on the battery itself or inside the bay; the oils on your fingertips could reduce the conductivity of the battery.
4. Take the replacement battery out of the box.
5. Slide it into the notch or bay.
6. Close the safety latch to lock it into place.
7. Reconnect the AC adapter and give the battery a full charge.
(Resource origin: http://www.dummies.com/computers/pcs/how-to-replace-your-laptop-battery/)