1. Turn your Gateway T6821c laptop over.
2. Find the laptop battery release button lock for your Gateway T6821c laptop.
3. Now that your Gateway T6821c 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 Gateway T6821c battery is removed, grab your replacement Gateway T6821c battery for installation.
6. Insert the battery into the slot. Push the Gateway T6821c battery towards the laptop and secure it in place.