Bucket Wheel Excavator not powering up?
As Phil B suggests you really must start by testing a motor by itself from the battery box. This will confirm whether that battery box is working or not.

My experience in Radio Control has taught me to test each "electrical" bit one at a time and in a logical sequence starting from the power source until the fault is identified.

For the future it worth testing electrical things like the motor and battery box before they get "built in" to a complex model.