Basically no manual selection. The power source is automatic, via an Auto-Transfer Switch (ATS). If the generator is running, it has priority as the power source and the ATS disconnects from shore power, whether the shore source is active or not. If you do not want the genset as power, then shut it off. That's your manual control feature. :
If you want to use battery & inverter only when shore power is connected, manually unplug the shore cord.
Battery power is always available unless you have activated the Storage disconnect. However, when either shore or genset is active, the converter/inverter/charger system provides a parallel source of 12v power so the batteries are online but not really contributing. As soon as external power goes off, the batteries resume supplying 12v.
Your inverter/charger also has an internal auto transfer switch. so it utilizes external power (shore or genset) when available but reverts to inverting battery power to supply selected 120v circuits as needed. If you do not want that to happen, you can turn the inverter off.
Some inverters have separate on/off for inverting and charging, while others have only a single switch.
