Power went out - which power? 120V AC, or 12V DC or both?
If both, then focus on getting battery data, install Lithionics Battery Monitor app on your phone, connect to your battery and make a screenshot. Swipe to the left from main app screen to get a Details List screen, take a screenshot of that too. Look at the battery On/Off button inside the compartment, near the breaker. Is the blue LED ring around the button lit up solid, off, blinking fast or blinking slow? If off, press the button to turn it back on, then connect from the app to take screenshots.
Is DC breaker in the on position, lever upward?
Take photos of what's showing on Xantrex panel and GoPower solar control panel, if anything.
Did you charge the battery before the trip from shore power? Did you somehow confirm that battery is fully charged?
With no details provided I can only assume that battery wasn't charged and simply ran out of power.