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I had a couple of Energizer "Industrial" 9v batteries - both had "6LR61" printed on the front or side, and they had 6 AAAAs inside. Once opened, nothing was soldered, so they just came right out! As noted elsewhere, polarity is reversed. However, they're a little bit shorter than conventional AAAAs, but I solved the problem easily by inserting a folded wedge of aluminum foil between the batteries.