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Size a backup battery around the devices you actually need.

Estimate daily energy, battery capacity, runtime, and inverter headroom from a multi-device load list.

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Your plan

01 / INPUTS

Devices (CSV)One row per device: Device, running watts, startup or peak watts, hours per day, priority. A header row is optional.Battery capacityWhEnter the advertised battery energy. Use a source specification, not a live price or catalog lookup.Usable battery fractionFraction of the nominal battery that you plan to use, written as a decimal from 0.01 to 1.Inverter efficiency%Planning assumption for battery-to-AC conversion. Check the product manual for the actual operating range.Planning horizondaysHow many daily load profiles the battery should cover.Inverter continuous ratingWContinuous output rating for the inverter or power station.Inverter surge ratingWPeak or surge output rating. It must be at least the continuous rating.

Illustrative example

Keep a copy of your inputsNo automatic saving. Files and photos are not stored.

LoadDay Power Planner

Calculated from user-entered inputs. Review assumptions and limitations.

Plan summary

02 / RESULTS

Live comparison

Running and peak demand

Running load125 W

Peak load220 W

Shared scale: 0 to 220 W. Values may overlap; bars are comparisons, not parts of a total. Review the details below.

Daily energy1,230

Battery needed for plan1,607.84

Estimated runtime at combined load6.12

Estimated coverage0.62

Running load125

Peak load220

Daily device energy and peak demand
Device	Running W	Surge W	Hours/day	Daily Wh	Priority
Wi-Fi router	20	40	24	480	Essential
Laptop	60	90	8	480	Essential
Small fan	45	90	6	270	Comfort

The entered battery does not cover the selected planning horizon at these assumptions.

Delivered energy uses 85% usable battery and 90% conversion efficiency.
A combined-load runtime of 6.1 hours is a planning estimate, not a manufacturer runtime guarantee.
Keep essential and optional devices in separate rows so you can remove lower-priority loads when power is limited.
Inverter headroom is 1075.0 W continuous and 2180.0 W peak.

Know the boundaries

Results use your entered load measurements and assumptions; they do not certify an electrical installation or guarantee a manufacturer runtime.
Battery aging, temperature, duty cycle, DC loads, and power-station reserve behavior can change real runtime.
Do not connect generators or transfer equipment without following the equipment manual and applicable electrical requirements.

Examples are illustrative. Results depend on the assumptions and measurements you enter.

Method, not guesswork

Start with the loads that matter during an outage, then separate their daily energy from their instantaneous startup demand. This keeps a large peak-wattage appliance from hiding an otherwise workable battery plan.

Read the methodology and worked examples

From inputs to a useful decision

All guides

Practical guide

Turn backup device loads into daily energy

Use running watts, hours per day, and priorities to build a transparent outage load scenario.

Read guide Practical guide

Compare battery capacity with inverter demand

Apply usable energy and efficiency assumptions, then check continuous and peak inverter inputs separately.

Read guide

Common questions

How is daily energy calculated?

Each row contributes running watts multiplied by hours per day, and the engine sums those watt-hours across the device list.

Why are usable fraction and efficiency separate?

The planner applies both assumptions to nominal battery Wh when estimating delivered energy and required battery capacity.

What does the inverter check compare?

It compares summed running watts with the continuous input and summed entered surge watts with the surge input.