# Usable kWh - Home Backup Power, Measured in Usable kWh

> Independent runtime math for home backup power: battery backup for one
> appliance at a time (sump pump, refrigerator, CPAP, well pump), whole-home
> sizing with or without solar, and portable power stations and solar
> generators ranked by USABLE watt-hours rather than the advertised number.
> Every product is scored on five criteria and human-reviewed before
> publishing. Product images come from retailer feeds, never AI-generated.

## What makes this different
Brands answer "will it run my appliance" about their own products. We answer
it with the maker's spec sheet, a stated inverter efficiency (85% unless a
sourced figure says otherwise), and the appliance's real running and surge
draw, then print the assumptions next to the number. Every appliance page
carries the same runtime table (hours on 1, 2, 4 and 8 kWh of usable battery,
running continuously and at a stated duty cycle). Every product card carries
the model number, the date the spec sheet was read, and the certification
status (UL 2743, UL 9540, UL 1973) or "none stated". When a maker does not
publish a figure we say so; we never guess or interpolate one.

## How we measure
Each product is scored 0-5 on Usable capacity (advertised Wh against what
reaches the outlet), Output headroom (continuous and surge watts against real
appliance starts), Chemistry and certification (LiFePO4 vs NMC, rated cycles,
UL status), Recharge and expansion (wall and solar recharge, pass-through,
expansion path), and Value and warranty (price per usable kWh weighted by
warranty years). See any review's "How we measure" section for details.

## Safety and scope boundaries
Hardwired work (transfer switches, interlocks, 240V circuits, panel work) is
described conceptually only and always handed to a licensed electrician; we
publish no wiring instructions. CPAP, oxygen and insulin pages are power math
only and make no medical claims. Gas generators appear only in comparisons,
with a carbon monoxide warning. Tax incentives are noted and linked to the
IRS and DSIRE, never computed for a reader. Nothing here is financial advice.

## Appliance backup (battery backup by appliance, with runtime tables)
- Battery backup for a refrigerator: how long a power station keeps food cold, from the EnergyGuide number (Hours a 1, 2 or 4 kWh power station keeps a refrigerator cold, sized from the EnergyGuide label, and five units with UPS switchover to do it unattended.): https://usablekwh.com/battery-backup-for-refrigerator/ [markdown: https://usablekwh.com/battery-backup-for-refrigerator.md]
- Battery backup for a space heater: do not do this, and here is what to do instead (A 1,500 W heater empties a 2 kWh power station in about an hour. The arithmetic from the heater's nameplate, and the loads that keep a person warm instead.): https://usablekwh.com/battery-backup-for-space-heater/ [markdown: https://usablekwh.com/battery-backup-for-space-heater.md]
- Battery backup for a sump pump: what actually works, sized from the pump's own numbers (Sized from a real pump's nameplate, not the box: which power stations run a 1/3 HP sump pump through a night of rain, and for how long.): https://usablekwh.com/battery-backup-for-sump-pump/ [markdown: https://usablekwh.com/battery-backup-for-sump-pump.md]
- Generator for a well pump: battery or gas, sized from the motor's locked-rotor amps (Franklin publishes 5 A running and 32.2 A locked rotor for a 1/2 HP well pump motor. What that means for a generator, and the two batteries that clear it.): https://usablekwh.com/generator-for-well-pump/ [markdown: https://usablekwh.com/generator-for-well-pump.md]
- Portable power station for a CPAP: how many nights, from ResMed's own power figures (Runtime for a CPAP with and without the humidifier, computed from ResMed's published draw, and five buyable units ranked for a night, a weekend and a week.): https://usablekwh.com/portable-power-station-for-cpap/ [markdown: https://usablekwh.com/portable-power-station-for-cpap.md]

## Whole-home backup
- Home battery backup: the three classes, what each actually runs, and how to size yours (Portable, expandable and installed home batteries compared on what they run and for how long, sized in kilowatt-hours per outage day from sourced figures.): https://usablekwh.com/home-battery-backup/ [markdown: https://usablekwh.com/home-battery-backup.md]
- Home battery vs standby generator: the same outage, two very different machines (Runtime, fuel, noise, start-up power and safety from the makers' own figures: a 22 kW Generac against Powerwall 3 and aPower 2, and when both is the answer.): https://usablekwh.com/home-battery-vs-standby-generator/ [markdown: https://usablekwh.com/home-battery-vs-standby-generator.md]
- How a transfer switch works, and why every backup source that feeds a circuit needs one (Manual and automatic transfer switches, interlocks, inlets and smart panels explained, why backfeeding is dangerous, and what an electrician installs.): https://usablekwh.com/how-a-transfer-switch-works/ [markdown: https://usablekwh.com/how-a-transfer-switch-works.md]
- Whole house battery backup: sizing an installed system, with or without solar (How installed home batteries are sized from your utility bill and your biggest motor, what Powerwall 3 and aPower 2 promise, and the without-solar case.): https://usablekwh.com/whole-house-battery-backup/ [markdown: https://usablekwh.com/whole-house-battery-backup.md]

## Best power stations by usable capacity class
- Best expandable power station: five systems that grow past 3 kWh, ranked on what they can start (The expandable class ranked on 240 V output, stated surge, expansion ceiling and safety listing: which systems start a well pump and which stay 120 V.): https://usablekwh.com/best-expandable-power-station/ [markdown: https://usablekwh.com/best-expandable-power-station.md]
- Best 1 kWh power station: five units for a day of essentials, ranked on the spec sheet (The 1 kWh class ranked on usable watt-hours, inverter headroom, UPS switchover and the cycle basis each maker actually states, every figure dated.): https://usablekwh.com/best-portable-power-station-1kwh/ [markdown: https://usablekwh.com/best-portable-power-station-1kwh.md]
- Best 2 kWh power station: five units ranked by what reaches the outlet (The 2 kWh class ranked on usable watt-hours, surge headroom, cycle rating and stated certification, every spec read from the maker's page and dated.): https://usablekwh.com/best-portable-power-station-2kwh/ [markdown: https://usablekwh.com/best-portable-power-station-2kwh.md]

## Head-to-head comparisons
- Anker SOLIX F3800 vs EcoFlow DELTA Pro Ultra: the two 240 V portables, one spec sheet each (The two portables that output 240 V from one unit, line by line from their makers' pages: capacity, output, what each states about surge and listings.): https://usablekwh.com/anker-solix-f3800-vs-ecoflow-delta-pro-ultra/ [markdown: https://usablekwh.com/anker-solix-f3800-vs-ecoflow-delta-pro-ultra.md]

## Outage plans and scenario guides
- 3-day power outage plan by house size: what to keep on, and how many kilowatt-hours that is (Four households, apartment to well-and-sump farmhouse, each with an essentials list in watt-hours a day and the battery class that covers three days.): https://usablekwh.com/3-day-power-outage-plan-by-house-size/ [markdown: https://usablekwh.com/3-day-power-outage-plan-by-house-size.md]
- Winter storm power outage plan: what to power, in what order, for how many days (A priority list in watt-hours: refrigerator, CPAP, phones and sump pump before anything that makes heat, with USDA food windows and three-day battery math.): https://usablekwh.com/winter-storm-power-outage-plan/ [markdown: https://usablekwh.com/winter-storm-power-outage-plan.md]

## Power math explainers
- Can you fly with a power station? The FAA's watt-hour lines, and what they mean for every unit on this site (The FAA's three watt-hour tiers for lithium batteries, why almost no power station clears them, the airline-approval band, and what a CPAP traveler packs.): https://usablekwh.com/can-you-fly-with-a-power-station/ [markdown: https://usablekwh.com/can-you-fly-with-a-power-station.md]
- How long do power stations last? Cycles, calendar years and the shelf, from the makers' own figures (What a cycle rating promises and to what capacity, how calendar aging and storage habits shorten it, and EcoFlow's published storage rules.): https://usablekwh.com/how-long-do-power-stations-last/ [markdown: https://usablekwh.com/how-long-do-power-stations-last.md]
- How many watts does a chest freezer use? Three ENERGY STAR sizes, and what they mean in an outage (Average draw for 10, 16 and 22 cubic foot chest freezers from their ENERGY STAR listings, the compressor start-up caveat, and USDA's 48-hour rule.): https://usablekwh.com/how-many-watts-does-a-chest-freezer-use/ [markdown: https://usablekwh.com/how-many-watts-does-a-chest-freezer-use.md]
- How many watts does a refrigerator use? Read it off the yellow label (The EnergyGuide method for a real average draw, two ENERGY STAR models worked through, and why the compressor's start-up spike is not on the label.): https://usablekwh.com/how-many-watts-does-a-refrigerator-use/ [markdown: https://usablekwh.com/how-many-watts-does-a-refrigerator-use.md]
- How many watts does a sump pump use? Four real pumps, from the nameplate (Running watts for four common sump pumps from the makers' spec sheets, the one published locked-rotor figure, and the math from watts to a night's watt-hours.): https://usablekwh.com/how-many-watts-does-a-sump-pump-use/ [markdown: https://usablekwh.com/how-many-watts-does-a-sump-pump-use.md]
- How many watts does a well pump use? Franklin's motor table, running and locked rotor (Running watts and locked-rotor start for 1/3 to 1 HP well pump motors from Franklin Electric's data, the duty cycle from real water use, and the battery math.): https://usablekwh.com/how-many-watts-does-a-well-pump-use/ [markdown: https://usablekwh.com/how-many-watts-does-a-well-pump-use.md]
- LiFePO4 vs NMC power stations: what the chemistry changes, in the makers' own numbers (Cycle life, weight, cold behaviour and what a cycle rating actually promises, compared on two Jackery units that differ mainly in chemistry.): https://usablekwh.com/lifepo4-vs-nmc-power-station/ [markdown: https://usablekwh.com/lifepo4-vs-nmc-power-station.md]
- Pass-through charging and UPS mode explained: leaving the battery plugged in so the outage finds it full (What pass-through charging is, how a power station's UPS mode differs from a real UPS, the switchover times makers state, and how to set one up.): https://usablekwh.com/pass-through-charging-and-ups-explained/ [markdown: https://usablekwh.com/pass-through-charging-and-ups-explained.md]
- Running watts vs surge watts: the number that trips a battery before capacity ever matters (What continuous and surge ratings promise, why motors spike at start-up, how to read locked-rotor amps, and why boost modes do not count for a pump.): https://usablekwh.com/running-watts-vs-surge-watts/ [markdown: https://usablekwh.com/running-watts-vs-surge-watts.md]
- Solar panel watts vs real charge time: why a 400 W panel is a 300 W panel, and what that does to your day (What a panel's rated watts mean, EcoFlow's own figure for real output, each power station's solar input ceiling, and the sun-hours a refill actually takes.): https://usablekwh.com/solar-panel-watts-vs-real-charge-time/ [markdown: https://usablekwh.com/solar-panel-watts-vs-real-charge-time.md]
- UL 2743, UL 9540 and UL 1973 explained: what a power station's safety listing actually covers (The three listings that matter for home batteries in UL's own scope language, why a UL94 flame rating is not one of them, and which makers state what.): https://usablekwh.com/ul-2743-ul-9540-explained/ [markdown: https://usablekwh.com/ul-2743-ul-9540-explained.md]
- Usable capacity vs advertised: why a 2,048 Wh battery delivers about 1,740 Wh at the outlet (Where the watt-hours go between the sticker and your appliance: depth of discharge, inverter loss and idle draw, and the formula the makers themselves publish.): https://usablekwh.com/usable-capacity-vs-advertised/ [markdown: https://usablekwh.com/usable-capacity-vs-advertised.md]
- Watt-hours explained for homeowners: the one unit every backup decision runs on (Watts, watt-hours and kilowatt-hours in plain terms, the conversions from amps and volts, and the two mistakes that oversize or undersize a backup battery.): https://usablekwh.com/watt-hours-explained/ [markdown: https://usablekwh.com/watt-hours-explained.md]

## EV charging at home
(none published yet)

## Tools
- Power station size calculator (tick appliances, choose days and a daily recharge including solar, get the class, usable Wh and the arithmetic; sourced wattages): https://usablekwh.com/calculator/

## Categories
- Appliance backup (battery backup by appliance, with runtime tables): https://usablekwh.com/category/appliance/
- Whole-home backup: https://usablekwh.com/category/whole-home/
- Best power stations by usable capacity class: https://usablekwh.com/category/roundups/
- Head-to-head comparisons: https://usablekwh.com/category/vs/
- Outage plans and scenario guides: https://usablekwh.com/category/scenarios/
- Power math explainers: https://usablekwh.com/category/guides/
- EV charging at home: https://usablekwh.com/category/ev/

## Related sites
- Rated Sturdy (weight-rated furniture and gear reviews, same publisher): https://ratedsturdy.com/
- Waterproof Sole (waterproof footwear reviews, same publisher): https://waterproofsole.com/

## Contact
- Email: hello@usablekwh.com