Aluminum bats are in baseball leagues, from little league all the way through college. It is very easy to cork an aluminum bat, which will make the ball travel a greater distance when it is struck. However, it is against the rules at any level, in any league, to use a corked aluminum bat. This would only be done for personal use and entertainment purposes. Corking an aluminum bat will give you an unfair advantage over your opponent.
Select an aluminum bat that you wish to cork. You will not be able to use the bat as a regular baseball bat after it has been corked, so do not use a new or expensive one.
Pop the top casing off of the aluminum bat. This will be quite difficult and it may take some time to achieve. Use the screwdriver as a wedge to separate the top from the bat.
Remove anything from inside of the bat. Aluminum bats are normally hollow, but little pieces of aluminum or dirt could become lodged inside the bat.
Drop the tennis balls inside the aluminum bat. Not all bats are the same length, so be sure to have enough tennis balls to completely fill the hollow area of the bat.
Put the top cap back on the bat. Try to glue it back as best you can. However, you can also cover the cap with duct tape to make sure it will hold.