Decision framework

Before you buy or hire

Measure firstUse the related calculator or confirm field measurements before comparing offers.
Who this guide helpsBackup Power readers who need a practical shortlist before spending money.
Product categories to researchPortable power stations, Expansion batteries, Compatible solar charging equipment
Do not skipFollow device manuals and carbon-monoxide safety guidance. Generators must stay outdoors and away from openings; medical-device users should confirm backup plans with providers.

Start with an essential-load inventory

List each exact load, model, power path, consequence of interruption, running watts, starting requirement, operating schedule, and priority. Separate must-run loads from conveniences and create distinct night, day, evacuation, and extended-outage bundles. A refrigerator, router, lamp, and CPAP are not automatically simultaneous. Food protection follows thermometer evidence, while a medical-device plan belongs with the provider and manufacturer; the energy worksheet cannot decide those safety thresholds.

Measure plug-in loads with properly rated equipment when manuals allow, ideally across full operating cycles. For hardwired, high-current, or safety-critical equipment, use qualified help or manufacturer data. Record whether watts are measured at AC input, DC input, or battery output because those numbers sit on different sides of conversion. The goal is a traceable inventory that another household member can reproduce, not a generic appliance-watt table.[1][4][3]

Keep power, energy, and surge in separate columns

Watts describe power at a moment; watt-hours describe energy across time. Continuous output determines whether the station can support all simultaneously running loads. Surge output is a short-duration pass/fail constraint for motors and compressors. The EcoFlow DELTA 2 and Jackery Explorer 1000 Plus publish rated capacity, continuous output, and surge output separately, illustrating why a single large number cannot answer both compatibility and runtime.

Check the exact output's voltage, waveform, current, port limit, shared-output limit, and surge duration or protection behavior. Add simultaneous loads for the continuous check and test each difficult start with realistic background loads. Do not convert a surge watt figure into sustained energy or assume a boost mode suits voltage-sensitive equipment. Runtime math begins only after every planned bundle passes the electrical compatibility checks in both manuals.[1][2]

Calculate usable energy before conversion

Begin with the rated watt-hours for the exact installed station and supported expansion batteries. Multiply by a documented or tested usable-capacity percentage that reflects charge and discharge limits. Do not quietly combine capacity with inverter efficiency; keeping them separate shows where assumptions enter. Expansion packs count only when the manual confirms compatibility, connection sequence, operating limits, and displayed combined state, and only after that configuration is tested.

Battery age, cycle history, state-of-charge limits, temperature, firmware, and protective shutdown can make a prior usable-energy result stale. Use exact manufacturer evidence rather than a universal derating factor. Hold a separate reserve for uncertainty and response time. A reserve is deliberately unused energy in the calculation, not evidence that the remaining battery is safe for indefinite storage or that a medical or food-safety threshold has been met.[1][2]

Move every load to the battery side

An AC appliance's measured watts are delivered-load watts. Estimate battery-side running power by dividing load watts by conversion efficiency expressed as a decimal. Add battery-side inverter or controller standby draw during off periods. Use evidence from the exact output path or a controlled input-versus-output test; efficiency varies with load and mode. A DC route can reduce one conversion stage but still has adapter and cable losses that need documentation.

For a cycling load, average battery power is duty times battery-side running watts plus one minus duty times standby watts. This prevents the common mistake of multiplying only appliance watts by duty while leaving the inverter awake for free. For multiple independent loads, calculate each schedule or use a measured combined profile. If the station times out at low load, determine whether the exact manual provides an approved setting for critical intermittent equipment.[1][2]

Apply duty cycle, reserve, and conservative scenarios

Raw runtime equals usable watt-hours divided by battery-side average watts. Planned runtime then multiplies raw runtime by one minus the selected reserve percentage. Calculate at the observed duty cycle, then raise duty by a meaningful amount and run a continuous-load case. The interactive tool uses entered, higher-duty, and continuous scenarios so readers can see how a cycling assumption changes the result without presenting one optimistic answer as universal.

Choose scenarios around consequences. A refrigerator plan should include warmer-room or recovery cycling and a separate USDA food-temperature response. A provider-approved CPAP setup should include its actual accessories and a relocation point, not a guessed low wattage. Network equipment may be nearly continuous. When several loads compete, make shedding rules explicit: what disconnects first, who decides, and which thermometer, alarm, or provider instruction triggers action.[1][3][4]

Build recharge as a separate timeline

Recharge does not belong in the runtime numerator until it is tied to time. Record the station's accepted solar voltage, current, connector, and maximum input; wall and vehicle limits; simultaneous charge-and-output rules; and the supported generator path. Then measure input watt-hours across the hours when it is realistically available. Panel nameplate watts multiplied by daylight hours ignores shade, clouds, orientation, heat, controller clipping, cables, and conversion.

Create a daily ledger with opening energy, load energy, measured recharge, reserve, and closing energy. Repeat with poor-weather and no-recharge cases. Expansion batteries increase the energy to refill, so they can lengthen autonomy while also making recovery slower. A fast wall-charging specification matters only when a safe energized source exists. Keep fuel-generator placement and connection safety separate from the battery's acceptance rate.[1][2]

Validate the result with the exact equipment

Run a supervised simulation using the exact station, battery configuration, ports, cords, settings, and loads. Start at the planned state of charge, log input and output, starts, duty cycle, faults, temperature indicators, and elapsed time, and stop at reserve. Compare delivered results with the worksheet, then revise usable capacity, conversion, standby, or schedule based on evidence. Test load-shedding and recharge steps instead of assuming they will be obvious during an outage.

Repeat after battery aging, firmware changes, accessory changes, a new appliance, altered settings, long storage, or a failed self-test. A station display provides useful operational information but is not an independent guarantee. For medical equipment, retain provider and manufacturer escalation. For refrigerated food, retain thermometer and USDA decision rules. The calculation supports those plans; it never replaces the underlying health or safety evidence.[1][2][4]

Use fuel generators only within the separate safety plan

A fuel generator can recharge some stations or support other loads, but it introduces carbon monoxide, fuel, heat, weather, noise, and electrical hazards. CPSC says operate portable generators outdoors only, at least 20 feet from homes, with exhaust facing away, never in a home, garage, basement, porch, shed, or partly enclosed area. Maintain working CO alarms on every level and outside sleeping areas. A charging cable does not relax those rules.

Confirm both manuals permit the charging source and stay within input limits. Never backfeed household wiring or improvise a male-to-male cord. Keep the generator dry using an approved arrangement without restricting exhaust or cooling, and refuel only as directed after shutdown and cooling. If the property cannot support safe outdoor placement or an approved connection, use a non-combustion plan or relocate rather than treating generator risk as hidden recharge efficiency.[5][1]

Compare products by evidence, not projected hours

A defensible comparison records rated and usable capacity, each port's continuous and surge limits, output waveform, idle draw, low-load timeout, charge limits, compatible expansion batteries, operating temperatures, protection behavior, cycle-life test basis, warranty, service, replacement path, and manual availability. Match those facts to the load inventory. More watt-hours do not correct an inverter that cannot start the critical appliance or a port that cannot support the required adapter.

Keep the article and tool roles distinct. This page owns the methodology, limitations, evidence collection, and interpretation. The dedicated runtime tool owns exact calculator intent and exposes every variable instead of hiding a fixed loss factor. Save inputs with dates and source documents, label defaults as examples, and present outputs as planning scenarios. Purchase only after the hardest credible case and a controlled test leave enough reserve for the household response plan.[1][2]

Portable runtime model inputs[1][2][3][4]
InputEvidenceCommon mistake
Usable WhExact battery settings/testUsing all label Wh
Running battery wattsMeasured load and conversionIgnoring inverter loss
Average wattsDuty plus standbyFree off-cycle time
ReserveChosen response marginPlanning to shutdown
RechargeTimed measured inputCounting panel nameplate

Sources and manuals

FAQ

What is the conservative portable power runtime formula?

Divide usable watt-hours by battery-side average watts, then apply the selected reserve. Battery-side average watts includes conversion loss, load duty cycle, and standby draw. Check surge separately.

Why does the calculator show continuous-load runtime?

It is a harder scenario that removes the benefit of cycling. It helps reveal when the plan depends too heavily on a calm-day duty-cycle estimate; it is not a prediction that every load will run continuously.

Do expansion batteries multiply runtime exactly?

Not automatically. Use only supported combinations, include the combined usable energy and losses, and test the configured system. Expansion also increases recharge energy and may change handling or operating limits.

Can I add solar watts directly to reduce the load?

No. Model solar as measured watt-hours arriving during specific hours within the station's input limits. Also run poor-weather and no-recharge scenarios before relying on it.

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