However, FedEx Corp. spokesman Rob Boulware says the batteries were nickel-cadmium.
Police Lt. Dan Christman say employees who were sorting packages were about 6 feet away from the cardboard box when it exploded. They reported a flash and a smell like gunpowder, but nobody was hurt.
The building was evacuated until a police bomb squad determined the cause of the blast.
Boulware says the only damage was to the package, and FedEx is working to identify the shipper.