Build separate average, running and startup loads using this page’s inputs.
Battery & Power
Estimate inverter battery backup time
Build the battery bank, enter the AC load and inverter losses, and estimate how long the selected charge range may support the load.
Calculation breakdown
Planning estimate only. Nominal current is not a cable or fuse sizing value. Confirm wiring, protection, inverter waveform, continuous and surge ratings, discharge data and battery-management limits before relying on the result.
Separate running, average and one startup event
Build a named appliance worksheet. Running watts assume every entered unit is on; average watts use the duty percentages you provide. Select only the rows starting together in one specific event. Example loads are illustrative, not appliance specifications. The original bank and runtime inputs are not overwritten.
Runtime, continuous load and startup are separate questions
The original form estimates runtime for a configured battery bank and entered AC watts or VA with power factor. The additional appliance worksheet separates all-on running demand, average energy demand and one specified simultaneous startup event. Averaging a cycling appliance’s consumption must not hide its higher running or startup requirement.
Describe the battery bank and conversion path
Bank V = voltage per battery × batteries in series. Bank Ah = Ah per battery × parallel strings. Nominal Wh = bank V × bank Ah. Selected energy = nominal Wh × condition fraction × (starting % − planned minimum %) ÷ 100. The planned minimum is a boundary you enter, not a detected low-voltage cutoff.
For apparent-power input, real watts = VA × power factor. Battery-side demand W = AC load W ÷ inverter efficiency fraction + separate inverter self-consumption W. Runtime hours = selected Wh ÷ battery-side demand W. Do not add self-consumption twice if your efficiency or measured battery draw already includes it.
One 12 V, 150 Ah battery used from 100% to 50% at full condition provides 900 Wh in that range. With a 300 W AC load, 90% conversion efficiency and 10 W separate self-consumption, battery demand is about 343.333333 W and linear backup time about 2.621359 hours. Lead-acid rate effects, changing voltage and real cutoff behavior can shorten or otherwise change that estimate.
Check W, VA and surge using the applicable rating
The Schneider Electric power measurement explanation distinguishes real and apparent power. Use the applicable manufacturer W and VA ratings rather than assuming the units are interchangeable.
The original optional ratings compare continuous watts, continuous VA when apparent load is known, and entered total startup watts against a surge-watt rating. The nominal battery-system voltage check is a system-class review, not an operating-voltage-window test. Current and C-rate outputs use nominal bank voltage. These comparisons do not verify battery/BMS current, surge duration or installation details.
Build an appliance worksheet
For each row, running W = per-unit running watts × quantity. Average W = running W × entered duty % ÷ 100. All-on running totals include every unit at its running watts even when its duty percentage is small. An illustrative 12 W continuous router and 60 W fan at 50% duty have 72 W all-on demand but 42 W average demand.
Running VA for a row is running W ÷ its known power factor. Adding those row values gives a conservative bookkeeping sum, not a calculation of net reactive power, phase cancellation or harmonics. The sum stays unknown if any positive-load row lacks power factor. Do not guess that every factor equals one. Enter the original VA rating in its apparent-power mode when needed; any entered rating is used by this separate worksheet. Continuous W and VA are compared with the all-on totals, independently of the average used for energy.
Define one startup event explicitly
Select the rows starting together and enter their total startup W per unit. For selected rows, startup demand replaces their running demand; it is not added on top of those same running watts. Other rows remain at all-on running demand during that event. All units in a selected row start together, so split a row if only some units start.
If the router remains on while the illustrative fan starts at 180 W, the event is 12 + 180 = 192 W. With two identical fans starting together it becomes 372 W. Missing startup watts for a selected active row leave the event unknown. No selected rows means no startup event was evaluated. The optional original surge-W rating is compared only when the event is known.
Apply the right total
Use a representative average watt figure for a linear energy/runtime scenario, while retaining separate all-on W/VA and startup checks. A 72 W average can coexist with 132 W all-on demand; a 75 W continuous rating would fail the latter. Duty percentages should include meaningful idle consumption. Measurements over a representative operating period are more useful than an unverified appliance preset.
The worksheet supports 1–20 rows, whole quantities up to 1,000,000, non-negative running/startup watts up to 1,000,000 per unit, duty 0–100% and known power factor greater than zero and at most one. Blank required fields are incomplete; blank power factors or startup figures remain unknown where applicable. Exact rational arithmetic precedes six-place display rounding. Source or row edits clear the prior result, and nothing is written back to the original form.
Neither method verifies startup VA, time-dependent surge capability, real efficiency curves or battery current limits. Use Inverter Battery Capacity for required bank sizing, Battery Series Parallel for whole-string stock allocation, or Battery C Rate for entered continuous-current constraints.