One appliance decides most of this purchase. Work out its daily kilowatt-hours first and the capacity you need falls out of the math.
Fridge runtime, calculated →A portable power station for home backup is a different purchase from the same box sold for camping. At a campsite it charges phones and runs a fan. In a house it is expected to keep food cold, keep a gas furnace blowing and keep a medical device alive overnight, and those loads are measured in kilowatt-hours, not phone charges. The specs that matter are capacity in watt-hours, continuous output in watts, and whether it produces 240 V at all.
What 1,000 watt-hours actually buys
Less than the label says, and for good reasons. The inverter that turns DC into household AC runs at roughly 85 to 90 percent efficiency, so about a tenth of the stored energy becomes heat. Manufacturers reserve some capacity at the bottom of the pack to protect cell life. And in cold weather, lithium chemistry delivers less than it does at room temperature.
The working rule: multiply the nameplate watt-hours by about 0.85 to get usable energy at the outlet. A 1,000 Wh unit delivers something like 850 Wh. Plan with the smaller number and you will never be unpleasantly surprised at 3 a.m.
Capacity against real loads
These figures assume a modern refrigerator at roughly 1.2 kWh a day, an older gas furnace with a PSC blower running intermittently in cold weather at roughly 3 kWh a day, and a CPAP with the heated humidifier switched off at about 0.3 kWh a night.
| Nameplate capacity | Usable | Fridge only | Fridge + furnace blower | CPAP nights |
|---|---|---|---|---|
| 500 Wh | ~425 Wh | 8-9 hours | Not realistic | 1-2 |
| 1,000 Wh | ~850 Wh | 16-18 hours | 4-5 hours | 2-3 |
| 2,000 Wh | ~1,700 Wh | 1.3 days | 9-10 hours | 5-6 |
| 3,600 Wh | ~3,050 Wh | 2.5 days | 17-18 hours | 10-11 |
| 6,000 Wh | ~5,100 Wh | 4 days | ~1.2 days | 17-18 |
Read the fourth column carefully. A winter outage is the scenario people buy these for, and it is exactly the scenario where a 1,000 Wh unit runs out before breakfast.
The fridge is a duty-cycle load
A refrigerator does not draw 150 W all day. The compressor cycles, typically running something like a third of the time in a cool room, more in a hot kitchen with the door opening. That is why the daily figure of 1 to 2 kWh is far lower than 150 W times 24 hours would suggest.
It also means you can stretch runtime by hand. Keep the doors shut, move what you need into a cooler, and the compressor runs less. A full freezer holds safe temperature for roughly 48 hours unopened and about 24 hours half full, which is the USDA guidance, so the freezer often does not need the battery at all for the first day.
The furnace question
A gas furnace stops in an outage because the blower motor, the inducer fan and the control board all need electricity, not because the gas stopped. Those are 120 V loads well within the output of a mid-sized power station. The complication is connection: the furnace is hardwired, so you either have an electrician fit a plug-and-cord kit with a switch, or you feed it through a transfer switch or interlock. Running an extension cord to a hardwired appliance is not a plan. The details are in running a gas furnace on a battery.
What these units genuinely cannot do
- Run a submersible well pump, unless the unit produces 240 V split-phase and has surge capacity in the 3,000 W range. Most do not, and the ones that do cost several thousand dollars.
- Run an electric water heater. A 4,500 W element would drain a 3,600 Wh pack in about forty minutes.
- Run resistance heating of any kind. A 1,500 W space heater is the fastest way to empty a battery ever devised.
- Run central air conditioning. Window units are borderline and depend on the compressor’s inrush.
- Refill themselves without either grid power, a generator, or panels and daylight.
Sizing bands that make sense
Under 500 Wh is a phone-and-laptop device. Useful, but it is not home backup and should not be priced as such. Between 1,000 and 1,500 Wh you get an overnight bridge: fridge, lights, router, devices, a CPAP for a night or two. This is the honest sweet spot for short suburban outages.
From 2,000 to 3,600 Wh you reach multi-day territory for a small critical list, and the better units in this band have output around 2,000 to 3,000 W, enough for a microwave or a well-behaved blower. Above 5,000 Wh with expansion batteries you are building a small home energy system, and at that price you should be comparing it honestly against a generator sized for the same loads, which will cost less and never run out of energy as long as fuel arrives.
Recharging is the constraint nobody plans for
A battery is a bucket, not a well. In a three-day outage the question stops being how big the pack is and becomes how fast it refills. Car charging through a 12 V socket is painfully slow, typically under 100 W. Solar input is limited by panel wattage and by daylight, and in a January storm there is not much of either, which is the whole subject of what the phrase solar generator actually hides. A small inverter generator running two hours to top up a battery, then shut off, is a quieter and far more fuel-efficient arrangement than either device alone.
Where I would put the money
For a house that loses power a few times a year for under a day, 1,500 to 2,000 Wh with at least 1,800 W of output covers the fridge, the lights and the internet without drama, and it does it silently and indoors, which a generator cannot. For a house that loses power for days at a time with a well and a furnace, the battery is the wrong primary tool and the right secondary one: pair a modest 1,000 to 2,000 Wh unit with a generator, run the generator in blocks, and let the battery carry the quiet hours. Two caveats before you buy: check the continuous output rating and not just capacity, and confirm the unit supports pass-through charging if you plan to keep it topped up while it works.
Frequently Asked Questions
What size power station do I need to run a refrigerator for 24 hours?
For a typical modern fridge at 1 to 2 kWh a day, plan on 1,500 to 2,500 Wh of nameplate capacity to comfortably clear a full day, and confirm the unit’s surge rating handles the compressor start, usually 600 to 1,200 W.
Can a portable power station run a whole house?
No, and units marketed that way are relying on a generous definition of house. They run a chosen list of loads. Well pumps, electric water heaters and resistance heat are outside what any portable pack does sensibly.
Is LiFePO4 worth paying extra for?
For home backup, yes. Lithium iron phosphate cells typically last a few thousand cycles against several hundred for older lithium chemistries, tolerate sitting at partial charge better, and are more thermally stable. For a device that spends most of its life waiting, longevity is the whole point.
Can I use one indoors while it charges from a generator outside?
Yes, and it is one of the better arrangements available. The battery lives inside where it is quiet and warm, the engine lives outdoors far from any opening, and you only run fuel a few hours a day.