Robin: "The car's not working."
Batman: "Did you check the battery?"
Robin: "What's a tery?"
Robin: "The car's not working."
Batman: "Did you check the battery?"
Robin: "What's a tery?"
This is a pun where Robin mishears "battery" as "tery". He doesn't know what a "tery" is, playing on the sound similarity. It's a silly play on words.