Inputs and units
The appliance checkboxes use the wattages shown beside them; they are not measurements of your equipment. Enter the capacity of the assembled bank in Ah at its bank voltage. Series connections add voltage while parallel strings add Ah. Choose the usable fraction appropriate to your battery and intended operating limit.
How the calculation works
Usable energy (Wh) = bank Ah × bank V × usable fraction × 0.85
Runtime (h) = usable energy / selected running wattsThe 0.85 factor is a fixed inverter-efficiency assumption. The running watts of all selected appliances are added, and the estimated usable energy is divided by that total. The same tool also displays a generator estimate, but its short starting surge is not the continuous load used for runtime. All selected loads are assumed to run continuously.
Worked example
Select only the 65 W laptop. A 200 Ah, 12 V bank with 50% usable depth provides 200 × 12 × 0.5 × 0.85 = 1,020 Wh after the assumed inverter loss. Dividing by 65 W gives about 15.7 hours. Adding a continuous 15 W router increases the load to 80 W and reduces the estimate to 12.75 hours.
Assumptions and limits
A refrigerator cycles, a laptop changes power draw and an inverter consumes some power even at light load. The tool does not model those effects, battery age, temperature, discharge-rate effects, cable loss, voltage sag or protective shutdown. An inverter may fail to start a motor even when the energy estimate looks adequate. The BeaconVault wattage preset is a planning assumption, not a verified product specification. Use measured loads and battery manufacturer data for a final power budget.
References and calculation details
Page prepared September 18, 2026. Examples describe this calculator’s implementation; reference links do not imply independent certification.