I once found a AAA battery inside a AA case. I don't remember where I got those batteries it may have been rechargables I bought on ebay or Walmart. Rechargable batteries that did not work as claimed, Eneloop batteries work great.
I used a Harbor Freight coupon to get a free bargain pack of AA batteries they are very light weight like balsa wood. They work but don't last long I cut 1 in 1/2 it was full of little white balls about 3/32" diameter. I never saw a battery built like that before.
I don't usually learn an item is trash until after I buy it and try it.