Yep, the 120 volt AC household outlets only work when connected to shore power, generator, or if you have an inverter connected to the battery.
Now you might have a few 12V dc outlets. They will work off the battery. They will look like the AUX outlets in your car, or a small 1/4" hole that looks like an old school headphone jack. Possibly integrated in the ceiling light or a special plug near the bunk ends again mounted on the ceiling.
Have a great trip