>In a house on the eastern side of town, if you head upstairs, there's a guy that will ask to see a Pokemon with the move Charge. However, it needs to be on a Pokemon from the opposite version — a Blitzle or something from your own version won't work, so you'll need to trade with a friend to get one. What do you get if you can do this? If you do this in either version, you'll wind up with a Cell Battery, which, after the holder takes damage from an Electric-type move, it raises the user's Attack afterwards (and uses up the Cell Battery).
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