Coding is required if you change the type of battery you are putting in the vehicle. For example if you are going from NON AGM to AGM or if you go from 70ah to 90ah. Then you will need to code the vehicle to tell it the new battery type you have installed.

Registration is required whenever a battery is changed essentially to sync both battery and vehicle.

While everyone will not need to code their new battery (depending on whether or not they change the type), registration is always required.

Some will argue that they do not need to register the battery and their car has been fine for x amount of time, but failing to do so may result in compatibility issues or battery drainage issues.