What is inside 6 V batteries?

You know the big square one you typically put inside lanterns. I just received a video showing how you can save money on batteries because if you peel off the label and pry open the top 32 AA batteries actually power the inside. Is this legit? If it is they are saying you can get 32 batteries for the price of about a 4 pack of AA's in the store. For about $5.