About 300 Wh covers phones, lights and a router; about 1,000 Wh adds a CPAP for several nights or a fridge for most of a day; and about 2,000 Wh with a solar panel extends fridge coverage. To estimate runtime, multiply the station's rated watt-hours by 0.85 and divide by the watts your device draws.
Power stations are sold by two numbers that are easy to mix up. Watt-hours (Wh) are how much energy the battery holds. Watts (W) are how much power it can deliver at one moment. The first decides how long things run. The second decides whether they run at all.
Sizing one for an outage is mostly arithmetic. Start with what you need to keep running, then work back to the battery.
The runtime formula
A workable rule is: hours = rated Wh × 0.85 ÷ load in watts. The 0.85 allows for the energy lost in the inverter and in conversion. It is an approximation, and devices that charge by USB or DC do slightly better.
For example, a 1,000 Wh station has about 850 Wh of usable energy. A 15 W router would run for about 57 hours. A device that draws 100 W would run for about eight and a half.
The watt figure you need is the average draw, and for anything with a motor or a thermostat that is lower than the number on the nameplate. A fridge compressor cycles on and off, so its average over a day is a fraction of its running wattage. An inexpensive plug-in energy meter will tell you the real figure for your own appliances.
What 300, 1,000 and 2,000 Wh actually run
The table applies the formula to typical loads. The load figures are estimates and vary widely between appliances, so treat the results as a guide and measure your own equipment where it matters.
| Load (typical average draw) | 300 Wh (255 usable) | 1,000 Wh (850 usable) | 2,000 Wh (1,700 usable) |
|---|---|---|---|
| Phone (about 12-15 Wh per full charge) | about 15-20 charges | about 55-70 charges | about 110-140 charges |
| LED lamp, 10 W | 25 h | 85 h | 170 h |
| Wi-Fi router and modem, 15 W | 17 h | 57 h | 113 h |
| CPAP without heated humidifier, 30-40 W | 6-8 h (one night) | 21-28 h (about 3 nights) | 42-57 h (about 5-7 nights) |
| CPAP with heated humidifier and tube, 70-100 W | 2.5-3.5 h | 8-12 h (about 1 night) | 17-24 h (2-3 nights) |
| Full-size fridge, averages 50-80 W, surge 600-1,200 W | 3-5 h, and may not start it | 10-17 h | 21-34 h |
| Chest freezer, averages 30-50 W | 5-8 h | 17-28 h | 34-57 h |
| Gas furnace blower and controls, 300-600 W running | no | 1.5-3 h of run time | 3-6 h of run time |
| 1/3 hp sump pump, about 800 W running, surge 1,300-2,900 W | no | about 1 h of pumping, if it starts | about 2 h of pumping |
In practical terms, a 300 Wh unit is a communications and lighting battery. A 1,000 Wh unit adds a CPAP for several nights or a fridge for most of a day. A 2,000 Wh unit gives a fridge more than a day and offers short furnace or sump coverage. None of these sizes is a multi-day furnace or sump pump solution without a way to recharge.
Surge loads: why a fridge may not start
Anything with a motor draws a brief burst of extra power when it starts. For fridges, freezers and pumps that surge is typically two to three times the running wattage for a second or so, and sometimes more.
Every power station has two output ratings: continuous and surge. If the appliance's start-up surge is above the station's surge rating, the station shuts off and the appliance does not start, however much energy is in the battery. Check the surge rating against your fridge or pump before you buy.
Why a furnace needs an electrician
A gas furnace needs electricity for its blower and controls, and the table shows that a large station can supply it for a few hours of run time. The obstacle is the connection. Furnaces are hard-wired into the house and have no plug.
Powering one from a portable source requires a transfer switch or an interlocked inlet installed by a licensed electrician. In Ontario that work needs a permit from the Electrical Safety Authority. Never feed power back into the house through a wall outlet. It can energize the lines outside and injure a utility worker, and it can destroy your equipment when grid power returns.
A furnace blower cycles, so a few hours of run time may stretch across a cold night. For a longer outage, plan to stay warm without the furnace as well. Our winter storm guide covers insulation and consolidating the household into one room.
Solar: summer versus December
A solar panel turns a fixed battery into one that refills, but the nameplate wattage is a best-case figure. Real output is typically 50 to 75% of it in good summer sun, and far less under cloud, low winter sun or snow.
As a rough estimate for southern Ontario, a 200 W panel yields about 0.6 to 1.0 kWh on a clear summer day and perhaps 0.1 to 0.3 kWh on a typical December day. These are estimates from typical sun-hours data and your site will differ.
- Summer: one 200 W panel can keep phones, lights, a router and a CPAP going indefinitely. A fridge needs roughly 1.2 to 2 kWh a day, so it takes 400 W of panels or more in good sun.
- December: the same panel may return only enough for phones, lights and a router. Do not plan winter heating or refrigeration around portable solar.
- Cold: most lithium batteries should not be charged below 0 °C unless the unit has battery heating. Keep the station indoors and run the panel cable through a window.
When a generator makes more sense
For long outages or heavy loads, a fuel-burning generator delivers far more energy than any portable battery, for as long as you have fuel. The costs are noise, maintenance, fuel storage and carbon monoxide.
A battery power station produces no exhaust, which is why it can be used inside, including in an apartment. For many households the sensible arrangement is a battery for the quiet, indoor loads and, where there is outdoor space and a real need, a generator placed well away from the building.
How to choose
- List what must run, and separate it from what would be convenient. Medical devices, communications and light come first.
- Find the average watts for each item, from a plug-in meter or the manual.
- Decide how many hours you want to cover. The Government of Canada's baseline is to be self-sufficient for at least 72 hours.
- Multiply watts by hours, add the results, and divide by 0.85. That is the watt-hours to look for.
- Check the surge rating against anything with a motor.
- Decide how it will recharge: solar, a vehicle, or a neighbour who still has power.
If you depend on powered medical equipment, also register with your electricity provider's medical or life-support program if it has one, and keep a plan for relocating. A consumer power station is not a medical-grade supply. For everything else an outage involves, see the power outage kit checklist and our power outage guide, or use the kit finder.
Frequently asked questions
How long will a 1,000 Wh power station run a fridge?
Roughly 10 to 17 hours for a typical full-size fridge that averages 50 to 80 W over a day. That comes from multiplying 1,000 Wh by 0.85 for conversion losses and dividing by the average draw. The station's surge rating must also be high enough to start the compressor.
Can a portable power station run a furnace?
A large station can power a gas furnace's blower and controls for a few hours of run time, but furnaces are hard-wired and have no plug. Connecting one requires a transfer switch or interlocked inlet installed by a licensed electrician. Never feed power into the house through a wall outlet.
Can I use a generator on a balcony or in a garage?
No. Health Canada says a fuel-burning portable generator must never be used indoors or in partly enclosed spaces, including the garage, and should be operated at least 6 metres (20 feet) from any home or building. A battery power station produces no exhaust and can be used indoors.
Sources
- Health Canada: preventing carbon monoxide exposure
- Government of Canada: how to prepare for a power outage
- Electrical Safety Authority (Ontario)
- Government of Canada: emergency kits
- Natural Resources Canada
General information only. Follow instructions from local emergency officials, and call 911 in a life-threatening emergency.