The additional 5A auxiliary charging output port is a new feature of the S+ model. It allows the user to charge a 12 volt charger battery in addition to the service batteries.
The Auxiliary Charge Module (ACM) is designed to be added to the circuit board of the Sterling Power ProCombi + inverter charger.
With the ProCombi S+ providing the charge to the service batteries the ACM will provide separate 5 map 12 volt charge to the start battery.