1. Turn your Sony VGN-CS209J laptop over.
2. Find the laptop battery release button lock for your Sony VGN-CS209J laptop.
3. Now that your Sony VGN-CS209J laptop battery is unlocked, find the battery release button down.
4. Holding the laptop battery release button, gently pull your battery away from the laptop.
5. Now that your Sony VGN-CS209J battery is removed, grab your replacement Sony VGN-CS209J battery for installation.
6. Insert the battery into the slot. Push the Sony VGN-CS209J battery towards the laptop and secure it in place.