Check if a UPS can handle your connected device load and runtime.
UPS ratings are quoted in volt-amps, which is not watts, and the gap between them is where most sizing mistakes live. A 1,500 VA unit with a 0.6 power factor delivers only 900 W — so a load that looks like a comfortable third of the rating can actually be well over half. Multiply the VA rating by the power factor to get the real watt capacity, then compare your load against it. Runtime is a separate calculation entirely: battery watt-hours times inverter efficiency, divided by the load. Note that runtime is highly non-linear — halving the load usually more than doubles the runtime, so shedding a monitor buys more time than the arithmetic suggests.
UPS Load Capacity
Usable watts = VA rating x power factor; utilisation = load / usable watts x 100; runtime min = battery Wh x efficiency% x 60 / load watts
Between 900 W and 1,500 W depending on its power factor. Check the watt figure on the label, not the VA number on the box.
Below 70-80%. That leaves headroom for inrush when equipment powers on and gives meaningfully longer runtime, since a lightly loaded UPS is more efficient as well as slower to drain.