Comparisons - CalmWatt

We compare home backup power stations the way a spec sheet cannot: side by side, on the same normalized measures, with every number traced back to the sentence the manufacturer printed.

Table of Contents

How our comparisons are built

Every number carries its source

Each specification in our database is stored with the manufacturer URL, the exact sentence the value was read from, and the date we checked it. A value with no source cannot be published — our tooling refuses to promote it. When we compared a widely circulated third-party spec table against manufacturer pages, seven of fifty-one values disagreed, including a recharge time that was off by a third.

We show you what the manufacturer will not say

Some specifications are simply not published. No manufacturer we have checked states how much energy you can actually draw from the outlet, as opposed to the rated capacity printed on the box. Several do not publish a UPS switchover time. One does not print the rated capacity in watt-hours anywhere on its product page. Where a figure is missing, our tables say manufacturer does not state rather than quietly borrowing a number from a review site.

Runtime is a range, and we show the arithmetic

Because usable capacity is never published, any runtime figure is a calculation, not a measurement. We give a range, state the conversion efficiency we assumed, and show the formula so you can substitute your own numbers. We do not bench-test these units and we do not claim to.

Starting current comes before running watts

A refrigerator, a sump pump and a furnace blower all draw far more current at the instant the motor starts than they do while running. A unit can have ample capacity and still fail to start the appliance. Where the surge rating falls short, our tables say the appliance is unlikely to start rather than printing a runtime the unit could never deliver.

Normalized measures, not raw ones

Bigger units win on raw capacity by definition, which tells you nothing. We rank on cost per watt-hour, watt-hours per pound, surge headroom, recharge rate and rated cycle life — and we always print rated cycle life together with the remaining-capacity percentage it is measured to, because 4,000 cycles to 80% and 4,000 cycles to 70% are different promises.

We say when a model is on its way out

Manufacturers retire models quietly. Where a product has been superseded or pulled from the manufacturer’s own catalogue, we say so and give the date we checked, because that changes whether a discounted price is a bargain or a dead end.

Available now

Generator carbon monoxide deaths: the CPSC revision matrix

Eight editions of the same federal report, compared. The first published count for a given year rises by an average of 51.5% in later editions. Free to cite, with the underlying data as CSV.

Start from the appliance, not the model

If you know what you need to keep running, these work the arithmetic backwards across every unit in our database.

What actually runs a gas furnace blower through a 12-hour winter outage — A gas furnace still needs its blower. We work out which units start it and how long they hold it.
What actually runs a refrigerator through a 12-hour outage — Which units carry a refrigerator for a full 12-hour outage, and which stall on the compressor’s starting surge.

Published comparisons

Comparisons in progress

Listed without links because the articles are not published yet.

Our full methodology, including what we will and will not claim, is set out in How we verify.