Backup power spec sheets throw a wall of units at you — W, Wh, Ah, V, surge watts — and manufacturers rarely explain how they relate. Here's the plain-English version of each one.
The core units
- Watt (W)
- A rate of power — how fast energy is being used or produced right this second. Think of it like speed: a 1,000W appliance draws power twice as fast as a 500W one.
- Watt-hour (Wh)
- A quantity of stored or used energy over time — power (W) multiplied by hours. A 1,000Wh battery can run a 100W device for 10 hours, or a 1,000W device for 1 hour. Think of it like distance traveled.
- Kilowatt-hour (kWh)
- 1,000 watt-hours — the unit your electric utility bills you in. 1,000Wh = 1kWh.
- Amp-hour (Ah)
- A measure of electric charge, common on car and RV batteries. Convert to Wh by multiplying by the battery's voltage: a 100Ah battery at 12V stores 1,200Wh.
- Running / continuous watts
- What an appliance draws once it's already operating normally — the number you add up for your baseline load.
- Starting / surge / peak watts
- The short burst a motor-driven appliance needs to start up, often 2-3x its running wattage — the number that catches most under-sized systems off guard.
- Volt (V)
- Electrical "pressure" — in the U.S., standard household outlets are 120V; some large appliances (dryers, some water heaters) use 240V.
How they relate to each other
The relationship that matters most: Watts × Hours = Watt-hours. If you know an appliance's wattage and how long you want to run it, you know exactly how many watt-hours of capacity you need. This is the entire basis of sizing a power station or generator correctly — see our free calculator for the version that does this math automatically across a whole appliance list, including the starting-watts spike most guides skip.
Why LiFePO4 keeps coming up
LiFePO4 (lithium iron phosphate) is the battery chemistry inside nearly every modern power station — it's more thermally stable and lasts roughly 3-5x longer (2,000-3,000+ charge cycles) than the older lithium-ion chemistry it replaced, which is a major reason portable power stations have gone from a niche product to a mainstream one over the last several years.