I think you can just solder the two pieces back together.
If you don't have a solder iron, have a beer from an aluminum can and cut a replacement from the (now empty) aluminum can

. The replacement doesn't need to be exact, as long as it can conduct electricity from the battery compartment.
You can also give conductive glue a try. You can get it from auto part store. It's the same glue used to fix heater element in car's rear window. If you don't know what it is, do a search for "conductive glue" or "wire glue."