Watts and watt-hours: the two numbers that matter
Watts (W) are power. Watt-hours (Wh) are energy. You need both to compare a battery with the equipment it will run.
Think of a reading lamp
An illustrative 10 W lamp running for six hours uses 60 Wh: 10 × 6 = 60. Two of those lamps use 120 Wh over the same period. A 1,000 Wh battery does not automatically provide 1,000 W of output; its energy capacity and output rating describe different limits.
Add energy; check power separately
If a 20 W networking setup runs for eight hours and a 60 W laptop runs for two, their combined use is 160 + 120 = 280 Wh. When both are on, their combined running power is 80 W. The planner assumes selected active devices may overlap for the output check, even when they are not all on for the entire outage.
Why a battery delivers less than its label
Conversion losses and the power station’s own electronics consume energy. The planner divides your device energy by an efficiency assumption, adds a separate battery-side idle-draw assumption, and applies a planning margin. Those defaults are adjustable estimates, not measured performance of a product.
What about mAh?
Milliamp-hours alone cannot be compared directly with watt-hours without a voltage. Wh = Ah × V, and Ah = mAh ÷ 1,000. For example, 10,000 mAh at a stated nominal 3.7 V represents 37 Wh before conversion losses. Use the manufacturer’s Wh specification when available, and do not assume the USB output voltage is the internal cell voltage.
Sources & further reading
Numerical examples and default device values are illustrative unless explicitly described as a measurement. Consult the manuals for your own equipment.
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