With 'Cut' in hand, you can now access Lt. Surge's Gym. The Gym entrance is blocked by a small tree, which you can now cut down. Lt. Surge's Gym has an electric fence puzzle. You need to find two hidden switches to open the door to Lt. Surge. The switches are hidden in trash cans. The first switch is random, but the second switch is always next to the first one.
Lt. Surge uses Electric-type Pokémon, which are weak against Ground-type moves. He uses:
- Voltorb (Level 21): Electric type.
- Pikachu (Level 18): Electric type.
- Raichu (Level 24): Electric type.
Your best strategy is to use a Ground-type Pokémon like Sandshrew or Diglett (found in Diglett's Cave, east of Vermilion City). Ground-type moves are super effective against Electric-types and Electric-type moves have no effect on Ground-types. After defeating Lt. Surge, he will award you the Thunder Badge and TM24 (Thunderbolt).