Watts (W) are how fast it uses power; watt-hours (Wh) are how much a battery holds. Runtime ≈ usable Wh ÷ watts. A Mini at 40 W Official spec: From a Starlink specification sheet or help article. Checked Oct 5, 2026 on a battery with 400 usable Wh runs about 9 h on USB-C.
Watts (W): the rate
How much power something is using at this moment. Starlink publishes the Mini’s average as 25–40 W Official spec: From a Starlink specification sheet or help article. Checked Oct 5, 2026.
Watt-hours (Wh): the tank
Watts × hours. A battery labeled 512 Wh could, in theory, supply 512 W for one hour or 51.2 W for ten. In practice you get less (next section).
Label Wh vs usable Wh
Some energy is lost converting the battery’s voltage to what the device needs, and batteries cut off before they’re completely empty. We plan with 85% of a power station’s label as usable Planning assumption: Our stated assumption, used until bench results replace it; our bench will measure real figures.
Volts (V) and amps (A)
Watts = volts × amps. USB-C at 20 V × 5 A = 100 W. The same 40 W at 12 V is 3.3 A; at 48 V it’s 0.83 A. Lower volts means more amps, and more amps means thicker wire (see voltage drop).
mAh: the number on power banks
Milliamp-hours at the cell voltage. Convert: Wh = mAh × 3.6 V ÷ 1,000. A 20,000 mAh bank ≈ 72 Wh.
Worked example (hypothetical)
- Load: 40 W (top of the Mini’s official range).
- At the battery, via USB-C: 40 ÷ 0.9 = 44.4 W.
- Battery: 256 Wh station, 85% usable = 218 Wh.
- Runtime: 218 ÷ 44.4 ≈ 4 h 54 min.
The calculator does this for you → · Glossary
Questions people ask
What’s the difference between watts and watt-hours?
Watts are how fast energy is used right now; watt-hours are how much is used over time. A 40 W load for 3 hours uses 120 Wh.
How do I convert mAh to Wh?
Wh = mAh × volts ÷ 1,000. Power banks rate mAh at the cell voltage (usually 3.6 or 3.7 V), so a 20,000 mAh bank is about 72–74 Wh, not 20,000 of anything you can use directly.
Sources
- Starlink Mini Specifications (PDF) · checked Oct 5, 2026