How to use
- Read the battery energy in watt-hours. If you only have milliamp-hours and volts, watt-hours is volts times amp-hours, and milliamp-hours are thousandths of an amp-hour.
- Read the lamp's watts on the setting you will use. A boost mode and a low mode are different runs.
- Press Calculate. The hero is hours.
- The gear checklist is where the lamp sits on the packing list. This page is only the runtime.
How it's calculated
Hours = watt-hours ÷ watts.
The page does not convert milliamp-hours. Do that before you type, so a 3.7 volt cell is not treated as if volts were optional.
Worked example
A 10 watt-hour battery and a 1 watt draw last 10 hours. The same battery at 2 watts lasts 5 hours. A 3.7 volt cell at 2,000 milliamp-hours is 3.7 × 2.0 = 7.4 watt-hours. At 1 watt that is 7.4 hours.
Assumptions
A constant draw and a battery that delivers its rated watt-hours. The page says in the result that cold and dimming change a real lamp. There is no temperature input.
FAQ
How do I get watt-hours from a phone-style battery?
Multiply volts by amp-hours. A label of 2,000 mAh is 2.0 amp-hours.
Why is the low mode longer?
Because you type a smaller watt number. The page does not know the mode names.
Does this include spare cells?
Only if you add their watt-hours into the battery number.
Is this the Ten Essentials list?
No. The gear checklist is that list. Runtime is this division.