Mentioned on Groups.IO that there can be an issue when inserting a new battery in the Duplex series of these throttles:
There is a fuse in line with the battery. If the battery is installed backwards, it will blow to protect the throttle.
When inserting AA cells, be careful, especially when inserting the middle cell: You can push down the contact tab, which can then short to the PCB underneath and again, blow the fuse.
If the fuse is blown, the throttle will work when connected to LocoNet, but not on battery power.