1. Turn your Toshiba P300D-21L laptop over.
2. Find the laptop battery release button lock for your Toshiba P300D-21L laptop.
3. Now that your Toshiba P300D-21L 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 Toshiba P300D-21L battery is removed, grab your replacement Toshiba P300D-21L battery for installation.
6. Insert the battery into the slot. Push the Toshiba P300D-21L battery towards the laptop and secure it in place.