What Size Portable Power Station Do I Need for an Outage?

Start with the consequence of losing power

Do not begin with a battery size. Begin with a short list of loads and what happens if each one stops.

Use three groups:

1. Must continue or needs a separate fallback: prescribed medical or assistive equipment, communication needed to obtain help, and any other load whose loss creates an immediate household-specific problem.
2. Important for a limited period: refrigeration, selected lighting, phone charging, a fan, internet equipment, or another load the household chooses.
3. Can remain off: high-draw or nonessential equipment that the plan does not attempt to support.

For medical or assistive equipment, use the device manufacturer, utility, clinician, supplier, or care plan to determine approved backup power and the point at which the person should move or seek help. This article does not determine that point.

Record two different numbers

Watts are power. They describe how much a device draws at a moment. A power station's continuous output must be high enough for the loads running together. Equipment with a motor or compressor may also require a higher starting or surge output.

Watt-hours are stored energy. One watt-hour is one watt supplied for one hour. Estimate a load's energy by multiplying its watts by the hours it will operate.

For example, a 40-watt load used for five hours calls for 200 watt-hours before accounting for conversion losses, cycling, temperature, battery age, or reserve. Use the power-station manufacturer’s usable-capacity and runtime information rather than treating the nameplate capacity as energy that will all reach the device.

Build a load table

For each intended load, record:

• device and purpose;
• running watts from the nameplate, manual, or manufacturer;
• starting or surge power when the device has one;
• expected hours of operation per day;
• whether it runs continuously or in cycles;
• approved connection or adapter;
• priority if power becomes scarce; and
• the fallback before it stops.

Add the running watts of devices that may operate at the same time. Compare that total with the power station's continuous output. Compare the largest relevant start-up demand with its supported surge output. Then total the estimated watt-hours for the desired period and compare that with usable stored energy and the recharge plan.

Test the plan before relying on it

A paper estimate is a screening tool. Connect only equipment the manufacturer permits, under ordinary supervision, and observe actual power draw and remaining capacity. Confirm that cords do not create a trip or heat hazard and that the planned arrangement does not block an exit.

Record the tested loads, test duration, remaining capacity, and any device that did not start or operate normally. Recalculate after adding a load or replacing the battery.

What not to do

• Do not choose capacity from a generic “days of backup” claim without the tested load behind it.
• Do not assume the watt-hour label is fully usable energy at every outlet and temperature.
• Do not ignore motor or compressor starting demand.
• Do not connect a portable power station to home wiring unless the product and a code-compliant installed system are specifically designed for it.
• Do not let a battery estimate replace a medical-device continuity plan or a decision to leave before essential support ends.

Next action

Record the loads that matter, their watts and operating hours, the available backup source, its continuous and surge output, its usable energy, its recharge method, and the point at which the household changes plans.