What Size Power Station Do I Need?

Most households need a power station between 1,500Wh and 2,500Wh with at least 1,800W of continuous output. That covers a fridge, internet, phone charging, lighting and a gas furnace blower for roughly a day. But the right number depends entirely on what you plan to run and for how long, and the arithmetic that gets you there takes about five minutes.

Quick answers by use case

If you want the short version, find your situation in the table below, then read on to check the reasoning. Every figure here already assumes you will lose 10–15% of the advertised capacity to inverter losses, which is covered in detail further down.

The mistake almost everyone makes

Nearly everyone shops by price. They pick the largest unit within budget, and then discover it either does not start what they needed or dies hours too early. Size is not a budget decision. It is an arithmetic one.

The reason the mistake is so common is that power stations are sold on one number — capacity in watt-hours — and that number answers only half the question. Capacity tells you how long. It tells you nothing about whether the thing turns on at all. Those are two separate specifications, governed by two separate parts of the machine, and a unit can be generous on one and hopeless on the other.

Work through the three steps below and you will end up with two numbers instead of one: a watt-hour figure and a watt figure. Shop against both.

Step 1: list what must stay on

Not what you would like powered — what genuinely must be. This distinction is worth being strict about, because it is usually the difference between a $600 purchase and a $2,400 one.

For most households in an outage the real list is short:

• The fridge and freezer. Not for comfort — for the several hundred dollars of food inside them.
• Internet and phones. Router, modem and chargers. Tiny loads with outsized value.
• Some lighting. A few LED lamps, not the whole house.
• Medical equipment. A CPAP, a nebulizer, an oxygen concentrator. Non-negotiable if it applies to you.
• Heat, in winter. If you have a gas furnace this means the blower only, which is a much smaller job than people assume.

What is usually not on the list: electric ovens, clothes dryers, central air conditioning, electric water heaters and anything else that makes heat with electricity. These are enormous loads, and a portable battery is the wrong tool for them. If you need those running you are looking at a whole-home battery system or a generator, not a portable unit.

Step 2: add up the watt-hours

A watt-hour is one watt drawn for one hour. Multiply each item by its average draw and the number of hours you need it, then add the results together. The word average is doing a lot of work in that sentence and is the most misunderstood part of sizing — see the fridge note below.

A typical “keep the essentials alive” day lands around 1,500–2,500Wh. That is why 2,000Wh units are the most popular bracket on the market. It is not marketing, it is where the arithmetic points for most homes.

Notice how cheap the small things are and how expensive the heat-producing things are. A router costs you a few hundred watt-hours across an entire day. A coffee maker costs a hundred watt-hours in five minutes. Anything with a heating element — kettle, toaster, hair dryer, space heater — will empty a battery faster than everything else on your list combined.

The fridge deserves its own paragraph

A fridge does not draw its rated wattage continuously. The compressor cycles on and off, typically running about a third of the time in a cool room, so a fridge with a 150W compressor averages something closer to 50W across the day. People who size using the label figure end up buying two or three times more battery than they need. This is common enough that we wrote a separate guide on refrigerator wattage, and it is worth reading before you commit to a number.

Step 3: check the inverter, not just the battery

Capacity decides how long. Output decides whether it starts at all. A 2,000Wh battery paired with a 1,000W inverter cannot run a 1,500W kettle for one second. It will simply refuse, or trip, and no amount of stored energy changes that.

Two output numbers matter:

• Continuous output — what the inverter sustains indefinitely, in watts. Add up everything you might have running at the same time and stay under this.
• Surge or peak output — a brief allowance, usually a second or two, for motors starting. Compressors, pumps and power tools draw three to seven times their running wattage at the instant they start.

That surge is why a fridge averaging 50W still needs an inverter rated far higher. The compressor might pull 600–1,200W for a fraction of a second every time it kicks in.

Most households want at least 1,800W of continuous output. 2,400W is comfortable. Below 1,000W you are limited to electronics and lighting, which is fine if that is genuinely all you need and a waste of money if it is not.

Why you never get the number on the box

Advertised capacity is the raw cell rating. What reaches your appliance is meaningfully less, for three reasons that stack.

Inverter losses

Converting stored DC into household AC costs roughly 10–15% of the energy. A 1,000Wh unit realistically delivers 850–900Wh to something plugged into its AC socket. Charging a laptop or phone from the DC or USB-C ports skips part of that conversion and is noticeably more efficient, which is worth knowing when you are rationing.

Cold weather

Lithium cells lose capacity as temperature drops. At freezing you might see 70–80% of the rated figure, and most batteries refuse to charge below 0°C entirely unless they have a heating system built in. This matters enormously if the battery lives in a garage, a van or an unheated basement, which is exactly where people tend to store them.

Age

Every battery loses capacity over its life. A LiFePO4 pack rated for 3,000 cycles to 80% means that after 3,000 full charges it holds 80% of what it did when new. That is a good result — older lithium-ion chemistries reach the same point in a few hundred cycles. Our chemistry comparison covers why the difference is so large and why it should shape your purchase.

Sizing by scenario

Weekend camping

Phones, a camera battery, a couple of lights, maybe a small fan. Realistically 200–400Wh across a weekend. A 300–500Wh unit is right, and the deciding factor is usually weight rather than capacity, because you will be carrying it. Anything above about 1,000Wh stops being genuinely portable for one person.

Car camping and overlanding

Add a 12V fridge, which is the big change: 300–600Wh per day on its own. A 1,000Wh unit gets you two days, and paired with 100–200W of solar you can stay out indefinitely in decent weather. Check the solar input rating before buying panels — some units accept far less than people assume, and the panel that came bundled is often not the one you want.

Van life and full-time off-grid

Here the arithmetic changes character, because you are not surviving an event, you are living a life. Budget 1,500–3,000Wh per day with a fridge, laptop work and Starlink. You want 2,000Wh+ of storage and 400W+ of solar, and you need to think about charge rates and recharge time rather than capacity alone. Our solar sizing guide covers the panel side properly, and the off-grid RV section covers the vehicle-specific parts.

A short power cut

Four to eight hours, a few times a year. You need the fridge, the router and some light: roughly 400–800Wh. A 1,000Wh unit is comfortable and costs a fraction of a home system. Honestly, for outages this brief the food in your fridge is fine without any intervention at all — an unopened fridge holds temperature for about four hours, and a full freezer for a day or more.

A multi-day outage

This is the scenario that justifies real money. Three days of essentials at 1,500–2,500Wh per day is 4,500–7,500Wh, which no single portable unit holds. Your options are an expandable system with extra battery modules such as the Bluetti Apex 300 or EcoFlow Delta Pro 3Check price on Amazon↗, a unit plus solar to recharge during daylight, or a permanently installed home battery. Solar is the part people skip and then regret — without a way to recharge, even a very large battery is a one-shot device.

CPAP and medical equipment

Size generously and buy a second charging route. A CPAP without the heated humidifier draws 30–60W, so a 1,000Wh unit covers two or three nights. Turning the humidifier off in an outage roughly doubles your runtime. If the equipment is genuinely life-sustaining, treat a battery as one layer rather than the whole plan, and ask your utility about a medical baseline registration, which in many areas gets your address prioritized for restoration.

When to buy expandable instead

If your answer sits near a boundary, or you suspect your needs will grow, buy into a system that accepts extra battery modules rather than a sealed unit at the top of your budget.

Expandable systems cost more per watt-hour at the entry point and less overall if you ever expand. They also let you spread the cost across years, which for a purchase this size is often the deciding practical factor. The catch is that you are committing to one manufacturer’s ecosystem — expansion batteries are not interchangeable between brands, and a discontinued line can leave you stranded. Buy expandable from a brand with a long product history and a large installed base.

You can see which units accept expansion batteries using the comparison tool.

Five sizing mistakes worth avoiding

1. Sizing on peak wattage instead of average. The fridge problem. It inflates your requirement by a factor of two or three.
2. Ignoring the inverter rating. Buying capacity you cannot use, because nothing heavy will start.
3. Forgetting the recharge. A battery with no solar and no generator is a single-use device in a real outage.
4. Including heat-producing appliances. Kettles, heaters and hair dryers belong on a generator or on nothing.
5. Sizing exactly. No headroom for cold, for age, or for the load you forgot.

Frequently asked questions