portable power station runtime formula

Runtime Methodology and Trust Policy

The site is useful only if the assumptions are visible. This page explains the runtime formula, source labels, unknown fields, and recommendation policy.

Runtime Formula

The calculator starts from nominal battery capacity, then applies the losses and assumptions that usually separate a label number from field runtime.

Usable energy

Usable Wh = nominal Wh x efficiency x reserve factor x battery health x temperature factor.

Runtime

Runtime hours = usable Wh / average load W. When a load has a duty cycle, average load W is running watts x quantity x duty cycle.

Range

Conservative and optimistic ranges show planning uncertainty instead of pretending that weather, duty cycle, load behavior, and conversion losses are exact.

Planning Assumptions

Tool defaults are shared across the site so the same setup does not get different answers on different calculators. These are planning assumptions, not product specs.

Output efficiency

Default conversion efficiency is 85% for AC inverter output, 90% for DC, and 92% for USB-C. Starlink-specific DC barrel and 12V step-up paths use 93% and 88% planning defaults.

Reserve and sizing buffer

Reserve stays user-controlled in the calculator. Size finder and emergency planner add a 15% sizing buffer after efficiency and reserve so a recommendation is not right at the edge.

Solar derate

Solar tools default to 75% derate, the Starlink field kit defaults to 70%, and outage planning defaults to 65%. Users should replace these with measured panel output or a site-specific PVWatts estimate when the plan matters.

Uncertainty ranges

The main runtime calculator and model-device pages build their conservative and optimistic runtime points by perturbing efficiency, reserve, battery health, temperature loss, and load. At the default AC assumptions this produces about 63% of the estimate on the conservative side and 124% on the optimistic side. Planning tools that need a simpler fixed envelope use 75% and 120% runtime factors instead. Solar yield ranges use 80% to 120%. Recharge time ranges are inverted because a conservative recharge estimate is longer, not shorter.

Source Confidence

Every model record can carry verified, estimated, or unknown confidence. The label should be visible wherever specs affect a result, and it is based on both source class and required spec completeness.

Verified

Required planning specs are present and backed by a manufacturer, manual, or official support source.

Estimated

The record is source-linked but has required spec gaps, relies on a retailer or editorial-only source, or needs stronger attribution before higher-trust recommendations.

Unknown

The site does not infer a precise spec when the available sources are missing or ambiguous.

Recommendation Policy

Model suggestions should come after the calculation. A station can be suggested only when the source-backed record clears capacity, output, and surge checks for the selected use case.

No active affiliate ranking is used in this phase. If commercial links are added later, they should be disclosed near the recommendation and must not change the calculation result.

Review Cadence And Corrections

This methodology is re-checked whenever planning assumptions, formulas, or confidence rules change, and station data is re-verified in dated passes recorded in the model data changelog.

Errors reported through the contact page are checked against the original sources before any published value changes.

Last reviewed: 2026-08-07.

FAQ

Use these policies when expanding into new tools, guides, and buying pages.

Is the runtime estimate a guarantee?

No. It is a planning estimate based on the inputs, source-linked specs, efficiency, reserve, battery health, temperature, and load behavior.

Why does WattRunTime.com keep unknown fields visible?

Unknown specs are safer than guessed specs. If a manufacturer page does not expose a precise port, surge, or input rating, the field stays unknown until a better source is found.

Do recommendations change because of affiliate status?

No affiliate ranking is active in the current phase. Future commercial links should be disclosed and kept separate from calculation logic.