Engineer-Joe posted:dead battery?
already in the system?
Yeah, you mentioned you have used them before, maybe they are on your "INACTIVE" Roster?
If not, try cleaning the pickup rollers and track as well as removing all other engines. I have found it a great habit to add trains to DCS on my test track and then moving it onto my layout, that way I can eliminate possible interference from other devices on my layout. Not saying interference is your issue but eliminating possibilities for failure helps find the issue.
Other than that, I would also check that the battery is charged but if I recall correctly, the battery being dead is more of an issue of possibly damaging the software in the engine vs not adding to DCS properly, in any case, its not a bad idea to check.
Good Luck!