Ignition key getting too hot

My daughter has a Hyundai Elantra 2000, which did not start last night. She brought it
In to the local Hyundai dealer and after they did their diagnostic they said it was a bad
battery. They replaced it and the car started up fine and my daughter drove it way. When she stop at home and turned off the ignition she found out that the ignition and the key were too hot even to touch it. Before the battery replacement the ignition was fine. What could have gone wrong by installing a new baterry?

Thanks

Josee Reis