Power station capacity tells you how much energy a battery stores. It is measured in watt-hours (Wh). Output, measured in watts (W), tells you how much power the station can supply at one time. You need enough of both.
This guide shows how to estimate runtime, choose a practical size, and compare backup-power options without relying on marketing claims.
Capacity vs. output
- Watt-hours (Wh): the stored-energy budget.
- Watts (W): the power a device draws or a station can deliver.
- Startup surge: the brief extra power some motor-driven appliances need when starting.
A station may have enough output to start an appliance but too little capacity to run it for long. The reverse can also happen: a large battery is not useful if its inverter cannot safely handle the load.
Simple runtime estimate
Use this planning formula:
Estimated hours = battery Wh × 0.85 ÷ average load W
The 0.85 factor is a practical allowance for inverter and system losses, not a guarantee. For example, a 2,000Wh station supporting an average 200W load works out to roughly 8.5 hours. Actual runtime changes with temperature, appliance cycling, battery condition, and other connected devices.
Choose capacity by what must stay on
| Need | Planning approach |
|---|---|
| Phones, lights, laptop | Add each device's watt-hours for the outage period. A smaller station may be enough. |
| Router and communication | Multiply average watts by the hours you want service, then add a loss allowance. |
| Refrigerator or freezer | Measure energy use over time and check startup requirements; one wattage reading is not enough. |
| Several essentials or a longer outage | Total the energy budget, decide how you will recharge, and compare expandable systems. |
Avoid the two common sizing mistakes
- Shopping by output alone. A high watt rating says little about runtime.
- Assuming nameplate watts are average watts. Refrigerators and other appliances cycle. Measure real energy use when possible.
Also check weight, charging time, ports, solar-input limits, storage location, and the exact accessories included with a package.
Compare the right capacity class
Start with the load and runtime math above, then choose the closest comparison: roughly 1kWh stations for a smaller essentials-focused setup, or roughly 2kWh systems for a larger energy budget.
Compare roughly 1kWh options Compare roughly 2kWh options
Affiliate disclosure: Big Prepping may earn a commission from qualifying purchases through retailer links. The comparisons are research-based, not hands-on tests. Confirm current prices, specifications, and package contents with the retailer.
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