Home Backup BasicsWatts vs. watt-hours, in one minute
Watts (W) is how hard something pulls power right now, like how fast water flows from a tap. Watt-hours (Wh) is how much is stored in the battery, like how much water is in the bucket.
Runtime ≈ battery Wh × 0.85 ÷ watts used. The 0.85 covers energy lost turning battery power into wall-outlet power. Example: a 1,000 Wh battery running a 60 W fridge lasts about 1,000 × 0.85 ÷ 60 ≈ 14 hours.
A phone sips power; heaters gulp it. That is why a small battery can charge phones for days but run a space heater for less than an hour.
Common questions
What is the difference between watts and watt-hours?
Watts (W) is how hard something pulls power right now, like how fast water flows from a tap. Watt-hours (Wh) is how much energy a battery stores, like how much water is in the bucket.
How do I estimate how long a power station will run something?
Runtime is about battery Wh x 0.85 divided by the watts used. The 0.85 covers energy lost converting battery power to wall-outlet power. A 1,000 Wh battery running a 60 W fridge lasts about 14 hours.
Why can a small battery charge phones for days but not run a heater?
A phone charger uses about 10 W while a space heater uses about 1,500 W, so the heater drains the same battery roughly 150 times faster.