How to Size a Portable Power Station
A practical four-step method for turning the devices you need into a usable battery capacity and output requirement.
1. List the devices you actually need
Start with the refrigerator, router, lights, phone charging, laptop, or medical device you need during an outage. Do not size around every appliance in the house.
2. Estimate energy
For each device, multiply running watts by the hours you need, then divide by about 0.85 for usable battery efficiency. For cycling loads such as a refrigerator, use the average duty cycle—not the compressor wattage for the entire period.
3. Check continuous output and surge
Capacity is only half of the decision. The station's rated AC output must exceed the appliance's running watts. For compressors, pumps, and power tools, compare the station's surge rating with the appliance's startup load.
4. Add reserve
Add 20–30% for battery aging, cold temperatures, inverter losses, and devices you forgot. A calculated 900Wh load is often a better fit for a 1,000–1,200Wh station than for a 900Wh battery.
| Goal | Typical planning range | Example use |
|---|---|---|
| Phone, laptop, router, lights | 300–800Wh | Short outages and camping |
| Refrigerator plus essentials | 1,000–2,500Wh | Multi-hour home outages |
| Longer home backup | 2,500Wh+ | Larger essential loads and longer runtimes |
Common mistakes
- Sizing only by Wh and ignoring output watts
- Forgetting startup surge for compressors and pumps
- Assuming the box capacity is fully usable
- Buying a station you cannot move or recharge