1. Turn your Sony VGN-CR21S laptop over.
2. Find the laptop battery release button lock for your Sony VGN-CR21S laptop.
3. Now that your Sony VGN-CR21S 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-CR21S battery is removed, grab your replacement Sony VGN-CR21S battery for installation.
6. Insert the battery into the slot. Push the Sony VGN-CR21S battery towards the laptop and secure it in place.