Electricity & water

Inverter & battery runtime calculator

How long could your backup power last with the things you plug in?

For appliances plugged into AC sockets. Watts (W) tell you how much power; watt-hours (Wh) tell you how much battery energy.

1 · What backup do you have?

Portable power stationBattery with AC plug socketsInverter & batteriesTrolley or separate battery bankUPS with AC socketsUninterruptible power supplyHybrid inverterBattery-only outage mode

I have a mini DC or USB-only UPS

How is battery capacity stated?Rated stored battery energy (Wh)

Use nominal stored battery energy from the label or manual, not VA or measured delivered AC energy.My capacity figure is measured delivered AC energy

Continuous AC output (W)

Find the continuous watts rating. VA isn't interchangeable with W.Peak AC output (W, optional)

Leave blank if unknown. Peak duration also matters.

I only know the VA rating

We need the battery capacity and continuous watts. Check the technical manual or manufacturer's runtime chart. We don't convert VA to W.

Present battery charge (%)

Starts at 100%: assuming fully charged. Change it to your present charge.Battery charge left unused (%)

Your minimum reserve. Check the battery manual; battery type alone doesn't set this.

Conversion, battery & startup assumptions

85% starts as an editable planning assumption. Idle draw starts unknown. These aren't measured equipment specifications.

AC conversion efficiency (%)

Conversion only, excluding the separately entered idle draw. A maximum rating may not apply at your load.Battery-side idle draw (W, optional)

Blank means unknown and omitted from the upper scenario. Enter 0 only as an intentional assumption.Battery health (%, optional)

Blank uses unreduced capacity with a warning; we don't guess ageing.Battery typeOutput waveform

I know the manufacturer's peak duration

Knowing the duration doesn't prove it is long enough for your appliances. We don't model start timing.

My efficiency figure already includes idle draw

2 · What will you run?

Choose appliances, then enter their watts. The tiles don't supply a typical rating.

Find an applianceAppliance group

Fibre ONT means the small fibre connection box. Include it separately if your internet needs both it and a router.

Your selected appliances (0)

All-ON running load: 0 W

Add appliances above, or try the hypothetical example.

3 · Your estimateAdd your battery capacityUse the separate running power, startup and energy checks below.

Inputs used — Charge 100%, reserve not entered%, conversion 85%, idle unknown (omitted).

Enter battery capacity.
Enter battery reserve.

Running power: 0 W / Not entered
Continuous rating check: Not checked
Startup check: Not fully checked
Nominal stored energy: Not entered
Planned usable stored energy: Not entered
Average non-brief load in scenario: 0 W

Your setup and appliances stay only on this page. Reloading or leaving clears them.

Where this comes from, and what it doesn't cover

AC battery planning for South Africa. Your label, manual and measured figures supply the equipment inputs. Hypothetical examples aren't appliance specifications.

EcoFlow's runtime testing guide suggests 80–90% conversion efficiency for a first estimate. The editable 85% starts at its midpoint.

Victron inverter specifications separate VA, watts, peak power and idle consumption. Victron's battery guidance explains reduced lead-acid capacity at high draw. Sources checked 11 October 2026.

Usable stored energy uses present charge minus reserve, adjusted only for entered health. Battery draw is AC load divided by conversion efficiency, plus entered battery-side idle draw.

We don't certify voltage, frequency, socket, waveform, start duration, battery protection limits or electrical compatibility. Check the manuals and test your actual setup.

This doesn't cover installation, wiring, solar generation, recharge, transfer behaviour, battery cycle life or product recommendations.

Inverter & battery runtime calculator

1 · What backup do you have?

2 · What will you run?

Your selected appliances (0)

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