If your software has read your communication bus...if the aux battery requires registration it will be listed just like the regular battery.
The registration of the new battery is due to the communication that goes on with it...which is mainly due to the IBS (intelligent battery sensor) connected to it which allows it to communicate with the car’s bus system. If your aux battery doesn’t have an IBS...then it probably won’t need to be registered which is probably why your software isn’t displaying a registration prompt for it.
Your AGM aux battery is monitored by a PCU (power control unit)...and again doesn’t use an IBS so there won’t be a need to register it...just the main service battery which DOES have an IBS.
