Portable Power Stations: How to Size One for a Power Outage

A portable power station is a big rechargeable battery with household outlets on the front. It is the quiet, fume-free alternative to a gas generator, and it is the thing people wish they had bought the week before the storm rather than the day the forecast turned. Late summer into fall is when this shopping usually starts: the Atlantic hurricane season runs through November and historically peaks from mid-September into October, and inland storm and wind outages follow their own autumn rhythm. Buying while you can think clearly beats buying while a cone of uncertainty is pointed at your county.

The catch is that these things are sold on big numbers that are easy to misread, and the wrong unit is an expensive paperweight. Below is how to size one from your own house rather than from a marketing bullet.

The two numbers that decide everything

Every station lists two figures, and they answer completely different questions.

• Watts (W) — the output. This is how much the station can deliver at one instant. It decides what you can plug in. A 300W station simply cannot run a 1,200W microwave, no matter how big its battery is.
• Watt-hours (Wh) — the capacity. This is how much energy is stored. It decides how long things run. Roughly: watt-hours ÷ the wattage of what you plugged in = hours.

So a 500Wh station with a 1,000W inverter can run a 1,000W appliance — for about half an hour. And a 2,000Wh station with a 300W inverter can keep a laptop and lights going for days but will refuse to start a fridge. You need both numbers to line up with your plan.

One more wrinkle: you never get the full rated capacity out through the outlets. Converting battery DC into household AC costs something, so plan on roughly 80–90% of the label reaching your devices. Subtract a bit more if the station's fan is running hard in a hot room.

Add up what you actually want to run

This is the ten-minute exercise that saves the purchase. Walk the house and write down what genuinely has to keep working, then find each item's wattage — it is usually printed on the appliance label, the power brick, or the manual. Typical ballparks for common household items:

• Phone charge: around 10–20Wh for a full top-up. A whole family's phones for a day is a rounding error against a big battery.
• LED lamp or lantern: roughly 5–15W each. Lighting is cheap; run it freely.
• Wi-Fi router and modem: often 10–25W combined — small, and worth keeping alive if your internet stays up.
• Laptop: commonly 45–100W while charging, less once topped up.
• Box or pedestal fan: roughly 40–100W. In a summer outage this often matters more than anything else on the list.
• Full-size refrigerator: commonly 100–200W while the compressor runs, with a much larger momentary surge each time it starts. Because it cycles on and off, a day is often in the 1–2kWh range — check the label on yours.
• CPAP: frequently 30–60W, more if you use the heated humidifier. Many people turn the humidifier off on battery for exactly this reason.
• Microwave, kettle, toaster, hair dryer, space heater: 1,000–1,500W and up. These are the appliances that force you into a large, expensive station — decide early whether you truly need them.

Now do the math twice. First, add the wattages of everything that could be running at the same moment — that total, plus headroom for surges, sets the output you need. Second, estimate a day's energy: multiply each item's watts by the hours you expect it to run, add it up, and that sets the capacity.

Surge is the spec people skip

Anything with a motor or compressor — a fridge, a freezer, a sump pump, a power tool — pulls a brief spike far above its running wattage when it starts. Stations list a continuous rating and a higher surge or peak rating for exactly this. If you plan to keep a refrigerator cold, look at the surge number, not just the headline watts, and give yourself real margin. A station that trips its overload protection at 2am is the failure mode you are trying to avoid.

The related spec is the inverter type. A pure sine wave inverter produces a waveform close to grid power, which motors, medical devices, and sensitive electronics prefer. Modified sine wave is cheaper and fine for a bare lamp, but it can make motors run hot and buzz, and some equipment refuses it outright. For outage use, pure sine wave is the safer default.

Battery chemistry: LiFePO4 vs. the cheaper stuff

Most current stations use one of two lithium chemistries, and the difference shows up over years rather than weeks.

• LiFePO4 (lithium iron phosphate): rated for several thousand charge cycles, tolerates heat better, and copes well with sitting near full for months between uses. Heavier for the same capacity, and usually pricier.
• Older lithium-ion (NMC and similar): lighter and cheaper, but typically rated for a few hundred to around a thousand cycles, and less happy in a hot garage.

For a unit that lives in a closet waiting for emergencies — which is most of them — LiFePO4 is generally the better long-run buy. For a lightweight camping battery you will replace in a few years anyway, the cheaper chemistry can make sense. Either way, check the manufacturer's storage advice: most recommend keeping the station partly charged and topping it up every few months rather than leaving it dead or pinned at 100% forever.

Recharging: wall, car, and the truth about solar

How you refill matters as much as how much you store. Three paths, with different realities:

• Wall outlet: the fastest option, and the one you will use 95% of the time. Look at the stated recharge time; fast charging is genuinely useful when a storm gives you a few hours of warning.
• Car 12V socket: slow — often a trickle — but it turns a running vehicle into a backup charger when the grid is down for days.
• Solar: the one that gets oversold. A folding panel almost never delivers its rated wattage for a full day, because angle, cloud cover, heat, and a single shaded corner all cut real output. Solar shines as a way to stretch a station across a multi-day outage, not as a fast refill.

If you do plan on solar, check the station's maximum solar input in both volts and amps before you buy panels — mismatched voltage is the most common reason a panel and a station will not talk to each other.

Ports, pass-through, and the small stuff that matters at 2am

Beyond the headline specs, a handful of details separate a station that is pleasant to live with from one that annoys you:

• Outlet count and spacing. Two AC outlets go fast. Chunky adapters can block a neighbor, so a station with well-spaced outlets — or a short surge protector plugged into one — saves fumbling.
• USB-C wattage. A 60W or 100W USB-C port charges a laptop directly without wasting energy on the AC inverter, which meaningfully stretches capacity.
• Pass-through charging. The ability to charge the station and power devices at the same time. Useful, but check the manual — some units discourage running it continuously.
• UPS-style switchover. Some models flip to battery in milliseconds when grid power drops, which keeps a desktop or a router from rebooting. Handy if your outages are brief and frequent.
• Noise and weight. Bigger inverters need fans, and fans are audible in a silent house. Weight climbs fast past 1,000Wh — look for whether it has a real handle or wheels if you will move it.
• A display you can read. Watts in, watts out, and time remaining, in the dark, without an app.

What a portable power station will not do

Being honest about the ceiling saves disappointment. A portable unit is not a whole-home backup. It will not run central air conditioning, an electric range or oven, a well pump, or an electric water heater — those loads are far beyond what a plug-in battery delivers. It also does not hardwire into your panel unless you buy a system explicitly built for that, with proper installation. Think of it as powering a room and a refrigerator, not a house.

It is, however, silent, produces no exhaust, and can be used indoors — which is exactly the opposite of a gas generator, and the reason many households now own both or choose the battery for lighter needs.

Rough tiers, so you can aim

• Under ~300Wh: phones, tablets, lamps, a router, a CPAP for part of a night. Light enough to carry one-handed and fine for camping. Not a fridge machine. If this is all you need, a large power bank may cover it for far less.
• ~500–1,000Wh with a 1,000W+ inverter: the practical sweet spot for most homes. Lights, devices, a fan, and meaningful refrigerator stints through a day-long outage.
• ~2,000Wh and up: multi-day planning, continuous fridge duty, occasional high-draw appliances. Heavy, expensive, and worth it mainly if your outages are long or you have medical equipment to keep running.

Whichever tier you land in, the rest of the outage kit is cheap by comparison: a reliable flashlight or two, a headlamp, and a charged power bank for phones cover the first hours before you even unpack the big battery.

A quick buying checklist

• Write down what must run, find each item's wattage, and total both the simultaneous watts and the daily watt-hours.
• Match output first (can it start the thing?), then capacity (how long will it last?).
• Check the surge rating if a fridge, freezer, or pump is on your list.
• Prefer pure sine wave output for motors and sensitive gear.
• Favor LiFePO4 for something you will own for years.
• Confirm recharge time from the wall, and the solar input limits if you want panels.
• Look at weight, handle, fan noise, and whether the display tells you what you need in the dark.
• Charge it when it arrives, then set a calendar reminder to top it up every few months.

Frequently asked questions