It turns out that Duracell, for reasons unclear, did not originally filed a trademark application for a “battery bunny” in the United States. Energrizer did in 1989, right after its ad debuted; Duracell tried to follow shortly thereafter. But it was too late — Energizer, the U.S. trademark holder, could block that action. That’s basically what they did. According to AdAge, “after Duracell filed for a U.S. trademark on its competing bunny, the two sides reached a largely confidential agreement in 1992 allowing Energizer to use the bunny in the U.S. and Duracell to use it elsewhere.”