Power Outage: The Calculation to Do Before Buying a Power Station

The blackout season is beginning. Wind, stubbornly clingy snow on the power lines, and the few hours without electricity that every winter bring to hundreds of thousands of French homes. The reflex has become buying a portable power station, those big wall-outlet battery packs sold for between €250 and €1,500.

The problem isn’t the product itself. It’s that almost no one calculates before buying, and product sheets deliberately keep a confusion between two very different things: the output power, expressed in watts, and the energy it contains, expressed in watt-hours. The former tells you what you can plug in. The latter tells you for how long. And it’s the latter that determines the device’s real usefulness.

Practical result: many households buy a €2,000 station expecting to get through winter, only to discover it heats nothing for more than an hour and ends up being used to recharge phones. Meanwhile others, with a well-spent €400, keep the heating running all night—an observation we revisit, because it’s the most useful takeaway of this dossier. We’ve gone through actual consumption by post, using roughly the same ballparks as those in our real-cost heating-energy comparison.

What a blackout really cuts from your home

Before buying anything, you need to know what goes out. The list is longer than “the lights and the fridge,” and it always surprises.

Heating, including gas and oil. This is the most unpleasant discovery. A gas boiler does not operate without electricity: its electronics, ignition, and especially the circulating pump that pushes hot water through radiators are all powered by the mains. A house heated with gas is thus cold during a blackout, just like a house that relies entirely on electricity.

Water, in some cases. A home fed by the public network keeps its pressure. A well with a booster pump, or an upper-floor served by a supply pump, loses running water.

Landline telephone. Telephony now runs through the box, hence through the mains. The old analog phone plugged into the line disappeared with copper.

The gate, the garage door, the rolling shutter. Each has a manual backup operation that is better learned before the outage than by the light of a flashlight.

Home medical devices. A continuous positive airway pressure (CPAP) device consumes roughly 30 to 60 W, while an oxygen concentrator consumes much more. If such a device is used in the home, the issue is handled with the medical provider that installed it, not with a product sheet: most have a protocol and a backup solution in place for this scenario.

The calculation no one publishes

A power station lists two figures. The output power, in watts, tells you what you can run without the device tripping. The capacity, in watt-hours, tells you for how long.

And you must subtract about 15% of the stated capacity: inverter efficiency, conversion losses, system reserve. A 1,000 Wh station effectively delivers about 850 Wh.

Here are the actual average consumptions for the important loads, followed by the corresponding autonomy.

The refrigerator line deserves explanation, because 15 W is surprising. A recent fridge-freezer consumes 100 to 150 kWh per year, i.e., 270 to 410 Wh per day. Its compressor draws 80 to 120 W but runs only about a third of the time on average: that’s the figure that matters for sizing a battery, not the peak. However, the power output of the station must cover the compressor’s startup spike, which briefly climbs much higher.

The gas boiler case, the one everyone misses

Look at the bold line in the table. It’s the most valuable information in this dossier and it doesn’t appear on any product sheet.

A gas boiler consumes about 100 W to run its electronics and circulator. The gas itself keeps arriving; the gas distribution network isn’t affected by an electrical outage. In other words, in a house heated with gas, 100 watts is enough to keep the heating running.

So a 1,000 Wh station maintains heating for eight and a half hours. A full night. For €600–€700, and the same station can also power lighting and phones once the boiler is turned off in the morning.

Compared with the “electric space heating” approach, which is the reflex of most buyers: the same 1,000 Wh station powers a space heater for about fifty minutes. That’s ten times less time, for just one room, instead of the whole house.

Three checks before counting on this solution. The actual power draw of your boiler when the burner is off, readable on the nameplate or in the manual. The fact that the hookup is accessible—many boilers connect to a standard outlet, some are wired directly and require a electrician to add an outlet. And the presence of a room thermostat, which consumes a few extra watts.

For a house heated by electricity, this reasoning does not apply: there is no reasonable home battery solution to run electric radiators. This is one of the rarely cited arguments in favor of gas, wood, or a non-electric auxiliary stove—a point we addressed from another angle in our analysis of so‑called economical radiators.

The freezer: the good news

It’s the number one worry, and it’s largely overestimated.

A full freezer, door closed, keeps its contents frozen for 24 to 48 hours without power. A chest freezer holds longer than a cabinet-style unit, and a fully loaded unit lasts longer than one that’s half empty—the mass of frozen goods itself serves as the cold reserve.

The rule is simple and free: do not open it. Not “open quickly,” not “just to check.” Do not open.

Powering a freezer with a battery makes sense only for a blackout announced to last more than 24 hours, or in a zone where outages typically run long. In that case, and only in that case, the row from the table becomes relevant and is favorable, with more than two days of autonomy on a 1,000 Wh station.

What a station will never do

Four uses to definitively rule out, because they are about power, not energy.

To heat. Any electric resistance heating draws between 1,000 and 2,500 W. A portable station, in this use, is a device with roughly an hour of autonomy. There is no consumer model that changes this arithmetic.

To cook. Hobs, oven, kettle, microwave: same family of powers, same conclusion. A camping gas stove for €25 does the job infinitely better, for forty times less cost.

To produce hot water. An electric water heater requires 1,500 to 2,400 W for several hours. Out of reach.

To power the entire house. Portable stations plug in device by device. Connecting a backup power source to the electrical panel is a fixed installation, which requires an electrician and a transfer switch, not a product you buy online and unpack during a storm.

What it actually costs

Price per watt-hour goes down as capacity rises, which mechanically pushes buyers toward overdimensioning. Here are the rough figures as of early October 2026.

The takeaway: the price gap per watt-hour between 300 and 2,000 Wh is about 20%, which is modest. The absolute price gap is €1,000, which is not. Overdimensioning costs little per unit of energy and a lot in absolute terms, and unused capacity yields no return.

Two criteria matter nearly as much as capacity and are less emphasized. The chemistry of the cells: lithium iron phosphate, LiFePO4, typically promises about 3,000 cycles versus 500–800 for traditional chemistries, a worthwhile consideration for a device meant to last ten years and serve three times a year. And the presence of a solar input, which turns the station into a usable back-up even off-grid during outages. We quantified the profitability of this approach in our plug-and-play solar kits dossier, and we tested a model combining both uses with the Jackery SolarVault 3 Pro Max.

For the models themselves, our Bluetti AC200L tests and our review of EcoFlow stations detail real-world behavior during charging and discharging.

The generator, and the danger that’s underestimated

For long-term autonomy, a gasoline-powered generator remains unbeatable: €500–€900 for 2,000 W continuous, with autonomy limited only by available fuel.

It imposes, however, a hard rule, and it kills every winter. A generator never runs indoors. Not in a garage, even with the door ajar. Not in a veranda. Not under a canopy attached to the house. Not in a cellar or basement. The exhaust gases contain carbon monoxide, a colorless, odorless gas whose early signs—headaches, nausea, drowsiness—mimic fatigue and push you to lie down instead of leaving.

The recommended safety distance is several meters from any opening, window, or vent, with the exhaust directed away from the building. And a carbon monoxide detector inside, around €20, is the logical complement to any generator.

The same precaution applies to diesel/gasoline space heaters that reappear on shelves each autumn: they require continuous ventilation of the room and should never operate in a closed bedroom.

Priorities list, by your home

Apartment, collective heating. The heating doesn’t rely on you and restarts on its own. A 30€ external phone battery and two €15 headlamps cover 90% of the real need. A 300 Wh station is enough if you work from home and want to keep the box online. Beyond that, you’re into comfort purchasing.

House, gas or oil heating. This is the scenario where a station is fully justified: aim for 1,000 Wh, identify the boiler outlet, and you’ll survive a blackout for a night without the house dropping. The best balance of usefulness and price in this dossier.

House, electric heating. No portable battery will heat your home. The trade-off moves toward a properly ventilated non-electric space heater, good duvets, and a modest station for lighting and communications.

Area with regular outages, or a home medical device. You move to a different problem category. A generator, or a fixed installation with a transfer switch by an electrician. And for the medical device, the protocol is built with the supplier who provided it, upstream.

Frequently asked questions

What capacity should a power station have for a blackout?

Between 300 and 1,000 Wh depending on the intended use. 300 Wh covers phones, lights, and the box for an evening. 1,000 Wh can sustain a gas boiler for eight and a half hours, or a fridge-freezer for more than two days. Beyond that, the absolute cost climbs faster than the real utility.

Does a gas boiler run during a power outage?

No, not without backup power: its electronics, ignition, and circulator are powered by the mains, even if the gas keeps arriving. It uses about 100 W, meaning that a 1,000 Wh station can maintain heating for a full night.

Can you heat a room with a portable power station?

Not effectively. A space heater draws 1,000 to 2,500 W: a 1,000 Wh station would power it for about fifty minutes. No consumer model changes this arithmetic. To heat, the option is a combustion heater with proper ventilation.

How long does a freezer last without electricity?

24 to 48 hours with the door closed, longer if it’s full and if it’s a chest rather than a cabinet. The only rule that matters is not to open it. Powering a freezer with a battery makes sense only for outages lasting more than a day.

Should you prefer a power station or a generator?

The station for short outages, quiet operation, and indoor use; the generator for long-term autonomy and high power. The generator imposes a strict rule: never indoors, never in a closed garage, stay several meters from any opening due to carbon monoxide.

What is the difference between watts and watt-hours on a power station?

Watts indicate the maximum power, i.e., what you can run without the device tripping. Watt-hours indicate the energy stored, i.e., the duration. It’s the latter value that defines real usefulness, and you should subtract roughly 15% for losses.

What we would do

Before buying: tour the home, make a sheet, and ask three questions. What heats my home, and does it depend on the grid? Where is my boiler connected? And what in my home cannot wait more than four hours?

In the vast majority of cases, the honest answer is: not much. Lamps, phones, and heating when it’s gas-powered. That is precisely what a 600–1,000 Wh station does very well, and what a €2,000 model does not do any better.

And if the budget is tight, the priority order is counterintuitive but solid: start with two headlamps and a phone-external battery, for around €50 total—this is what helps every blackout. Then, and only then, the station. Many households have done the reverse and found themselves hunting for a flashlight next to a €1,500 battery.