Enter a constant load
Use battery capacity in Wh and the combined device load in W. The tool assumes a constant load and no solar input. For cycling devices, a measured average load is more useful than treating the peak label rating as constant.
Understand the assumptions
Efficiency is entered as a percentage and applies to conversion losses. Reserve is capacity you plan not to use. Inverter idle draw is separate power consumed at the battery. Avoid counting idle consumption twice if your measurement already includes it.
Check an example
With 1,000 Wh, a 60 W load, 85% efficiency, a 10% reserve and zero idle draw, the result is 12.75 hours, rounded to 12.8 hours. The result does not verify output compatibility or account for changing loads, temperature and battery age.