W vs. Wh vs. Ah: Size a Portable Power Station

Separate power from energy

A watt is a rate of power. If a 100 W device runs continuously for 3 hours, its ideal energy use is 300 Wh. Two identical devices would use 600 Wh over the same period.

A 600 Wh battery does not normally deliver all 600 Wh to an AC appliance. The inverter, wiring, battery-management system, standby load, temperature, and battery condition all affect usable energy.

Do not compare Ah without voltage

The basic relationship is Wh = V × Ah. A 100 Ah battery at 12 V is theoretically 1,200 Wh, while 100 Ah at 24 V is theoretically 2,400 Wh. The Ah number alone does not tell you how much energy is stored.

For a packaged portable power station, use the manufacturer’s nameplate Wh as the starting capacity. If the manufacturer publishes measured AC-delivered energy, do not subtract the same conversion loss twice.

Build a planning estimate

Start with each device’s label or manual. Add the energy for every device, account for the AC or DC conversion path, then add a reserve for schedule changes and uncertain conditions. Round up to an available capacity rather than down.

• Device energy: W × quantity × hours × duty cycle × days
• Battery withdrawal: device Wh ÷ path efficiency
• Planning capacity: battery withdrawal ÷ usable fraction × reserve factor
• Use a measured wattage or cumulative Wh when available; labels and manuals take priority over category averages

Check output separately from capacity

Wh answers how long the battery may last. Continuous and surge W answer whether it can start and run the load at all. A large-capacity station can still be incompatible if its 120 V AC output, continuous wattage, surge duration, plug, grounding, or waveform does not meet the appliance requirements.

U.S. planning limits

• CampWatt provides planning estimates, not guaranteed runtime. Actual results vary with the device, duty cycle, conversion losses, temperature, battery age, and power-station settings.
• For U.S. AC use, verify that the appliance and power station support 120 V / 60 Hz, the physical plug and grounding arrangement, and any manufacturer-specific waveform requirements. A plug adapter alone does not convert voltage or frequency.
• Do not use this calculator or these guides to size, certify, or guarantee power for medical or life-sustaining equipment. Follow the equipment manufacturer, your care provider, and your emergency backup plan.