So you know the capacity of your UPS or Power Station, you know the load on the device, and you want to find out how long it'll run before the battery dies. Look no further.
Output voltage of 110V is assumed on Ah calculations.
Device efficiency is assumed to be 90%, for some wiggle-room.
Do not try to run anything mission-critical like your grandmother's ventilator or something solely based on these approximate results, because that's just a recipe for disaster.
You can calculate needed battery capacity with the UPS Battery/Power Inverter Capacity Calculator