This old abandoned building still has a few items lying around, but beware: some of the items are actually Voltorb and Electrode in disguise. Just past the entrance room is a Carbos, and further along is a second "item", a Voltorb. The room to the right is a dead-end with both a Voltorb and Electrode, just waiting to pounce on an unsuspecting Trainer. Continue south to the exterior wall, and pick up TM33 (Reflect). Head to the east, and grab TM25 (Thunder) in the southeast room. Follow the narrow hallway to the north and west to find a Rare Candy and an HP Up in the northeast room. Continue west and zigzag a bit to reach the final room.
Zapdos makes its nest in the deepest room of the Power Plant. Like with Articuno, save your progress before battling it. It won't go down without a fight, so whittle its health down and try inflicting a status condition before attempting to capture it.
Once the battle is done, take the side exit, and fly back to Viridian. It's time to claim the final badge!
VIRIDIAN CITY POKéMON GYM
In the time it took to collect the seven other badges, the leader of Viridian Gym has finally returned. None of the locals seem to know the identity of this mysterious figure, but it's certainly a familiar face.
Congratulations on defeating the eighth and final Gym! The Earth Badge commands attention of all Pokémon, regardless of level. Giovanni gives you TM27 (Fissure), a TM he claims to have made when he originally acted as Gym Leader. He seems remorseful of his actions with Team Rocket, and he officially disbands the gang before disappearing.
With all eight Gym badges collected, the way to Indigo Plateau is finally open. Gather a team with access to Surf and Strength, and stop by a Poké Mart to replenish your supply of Potions and Ultra Balls. The elite Trainers at Indigo Plateau are tough enough, but you'll never defeat them if you can't first get through Victory Road, a grueling tunnel with the third legendary bird roosting deep inside.