If you are flying under recreational/hobbyist rules, then you do not need to register each individual drone. You DO however need to put your FAA recreational ID number on each drone. Use the same number on each one.
If you are flying under Part 107 rules then each drone (that you use for Part 107 flights) must be individually registered and have its own ID number on it.
In either case, your new drone must have a FAA ID number displayed on the outside of the drone.