That is correct, giving the LM "track power" (which could even be as simple as a non-dead 9v battery btw) will power up the LM, nothing else needs to be connected for it to respond and downloaded to etc.
Now, are the LM's brand new (ie, bought from a retailer) or second hand? if second hand even if the HC still doesn't detect the LM's they may not be faulty but the previous owner could have put a password on them, which can be cleared in following the instructions in the HC manual.
- Tim