6000xp in UPS mode without cycling battery

It should automatically detect it; however you can manually set it to 120/208 through the application settings on the Monitoring website, or you can use setting #4 on the inverter screen to set it.

You can set the AC First start time from 00:01 to 23:59 to allow AC power to run the loads all day and preserve the battery. Keep in mind this is an off-grid inverter, so it primarily relies on battery and solar, but using the grid to power the loads throughout the day is possible.

I'm trying to accomplish the same thing (6000xp + battery, fucnting as UPS, no PV connected) but struggling with the settings. If I place the inverter in AC charge mode, the inverter continuously cycles between charging and discharging the battery. If I place the inverter in AC first mode as suggested above, the battery does not charge at all even after grid power comes back up after an outage. Is there a setting to have charging occur in AC first mode (but with no PV connected)?

When you set AC Charge, set it based off SOC, so this way the inverter will charge batteries with grid when the batteries go under a certain battery percentage, and you can still have AC first configured to power loads. This configuration is a little difficult to achieve as the 6000XP is an off-grid inverter, which primarily relies on battery and PV to power loads.