Sizing a Portable Power Station for a Power Cut

Portable power stations are bought on capacity and fail on output. The two are different numbers answering different questions, and confusing them is why people end up with a large battery that refuses to start their fridge.

Capacity and output

Capacity, in watt-hours (Wh), is how much energy is stored — how long it runs something.

Output, in watts (W), is how much it delivers at once — what it can run at all.

A station with a big battery and a modest inverter will power a laptop for days and refuse a kettle. One with high output and a small battery runs the kettle briefly. You need both checked against your actual needs.

Work out your real outage load

List what genuinely must stay on. For most households in a multi-hour outage that is a fridge or freezer, phone and laptop charging, some lighting, the router and modem, and any medical equipment. It is emphatically not the whole house.

To size capacity, multiply each item's wattage by the hours you need it, then add roughly 15% for conversion losses — the usable figure is always below the rated one.

The one that trips people up is the fridge. A fridge does not draw its rated power continuously; the compressor cycles, running perhaps a third of the time depending on ambient temperature and how often the door opens. So a fridge with a 150W running draw uses far less over 24 hours than the arithmetic suggests. Use the appliance's own energy label figure where you can, since it reflects real duty cycling.

Surge is the specification that decides whether it works at all

This is the most important paragraph here. Anything with a motor or compressor — a fridge, a freezer, a pump, a power tool — draws several times its running wattage for a fraction of a second at startup. A fridge that runs at 150W might demand 600W or more to start.

If the station's surge rating cannot cover that instant, the appliance simply will not start, no matter how large the battery is. Check the surge figure explicitly, not just continuous output, and check how long the unit can sustain it. This is the single most common reason a power station fails to run the thing its owner bought it for.

Battery chemistry decides how long the unit lasts

LiFePO4 is rated for thousands of charge cycles — commonly 3,000 or more to 80% of original capacity — and is more thermally stable. NMC is lighter and more energy-dense, and typically rated for several hundred cycles.

For a unit kept for outages and used occasionally, LiFePO4 is worth insisting on. It also holds up far better to sitting at partial charge for long periods, which is exactly what a backup unit does. Most current mainstream models have moved to LiFePO4, but confirm it on the specific product rather than assuming.

Recharging during a multi-day outage

A power station is a battery, not a generator — it makes no energy. In an outage longer than its capacity, how you refill it becomes the whole question.

• Solar is the realistic answer for a long outage. Note that real output is well below the panel's rating in anything less than ideal sun, so plan on substantially longer than the arithmetic suggests. Check the unit's maximum solar input, which caps how much panel you can usefully connect.
• Vehicle charging via a 12V socket is slow; some units support faster DC alternator charging.
• AC from the wall is fastest but requires the power to be back.

A practical point that gets overlooked: keep the unit charged. A backup device discovered at 20% when the lights go out is not a backup. Most manufacturers recommend topping up every few months, and units with app monitoring make that easier to remember.

What it will and will not run

Setting expectations clearly. A mid-sized station will handle a fridge, lights, routers, phones, laptops and most medical devices through an outage of hours to a couple of days.

It will not run central air conditioning, an electric oven, an electric water heater or a whole house. The units that approach that are large, expensive and effectively installed rather than carried. High-draw resistive appliances — kettles, hairdryers, space heaters, toasters — will run briefly on a large unit and drain it fast, and are worth doing without.

On pure sine wave: most reputable units produce one, and it matters for sensitive electronics and medical equipment. Cheaper units sometimes produce a modified sine wave, which some devices tolerate poorly — check if you are running anything medical.

Why not just buy a generator?

A fuel generator produces far more power for less money and runs as long as you have fuel. The reasons to prefer a power station are specific and, in one case, a safety matter.

A power station is silent, produces no exhaust, needs no fuel stored, requires essentially no maintenance, and — critically — can be used indoors. Running a fuel generator in a garage or any enclosed space is a recognised cause of carbon monoxide poisoning, and people die of it during outages every year.

For a household wanting to keep a fridge and some devices running through a storm, that trade is usually worth the lower capacity. For running a whole home for days, a properly installed standby generator is the right tool.

The practical details

Weight matters if you will carry it — around 25 to 30 pounds is typical for a 1,000Wh unit, and larger ones become two-person items. Cooling fans run under load and while fast-charging, and some units are loud enough to matter in a bedroom; many offer a quiet charging mode. And check whether the unit supports pass-through, charging and discharging at once, which matters for continuous backup.

If you are comparing units, our ranked comparison of portable power stations covers how the leading brands differ on capacity, chemistry and recharge speed, scored against the criteria in our rating methodology.

Specifications, chemistry and warranty terms vary by model and generation. Confirm current details with the manufacturer, check surge ratings against anything with a motor, and consult a qualified electrician for any permanent backup installation.