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Watts vs watt-hours (W vs Wh) on a power station, explained

Updated November 14, 2026 · 6 min read

The water tank way to think about it

Picture a water tank with a tap. The size of the tank is the watt-hours: how much energy is stored. The width of the tap is the watts: how fast energy can flow out.

A big tank with a narrow tap lasts a long time but can't fill a bucket quickly. That is a large battery with a small inverter: great for a CPAP all weekend, useless for a microwave. A small tank with a wide tap fills the bucket fast but runs dry quickly. That is a small battery with a big inverter: it will boil a kettle once or twice, then it is empty.

Every power station lists both numbers, and you need to check both.

How to work out run time

Divide the usable watt-hours by the watts your appliance uses:

Why 0.85? Battery power is DC. Your wall plugs need AC. The inverter inside the power station does that conversion and loses some energy as heat, typically 10–20%. So a 1,000 Wh unit gives you roughly 850 Wh at the AC sockets. USB-C and 12V outputs skip the inverter and lose less.

Use the appliance's average watts, not its peak. A fridge compressor might pull 150 W while running, but it switches on and off, so over a whole day it averages closer to 60 W.

What 1,000 Wh actually runs

Here is what a typical 1,000 Wh power station (about 850 Wh usable from the AC sockets) runs on a single charge. These are estimates from typical appliance ratings; your appliances will differ.

The pattern: anything that makes heat (heaters, kettles, hair dryers, microwaves) drains a power station fast. Anything that keeps something cold or connected is where power stations shine.

Want this for your own list of appliances? The power station size calculator does the sums.

Surge watts: the third number

Most spec sheets show two watt figures, for example "1,800 W continuous / 3,600 W surge".

• Continuous (rated) watts: what the unit can supply for as long as the battery lasts.
• Surge (peak) watts: what it can supply for a split second.

Surge matters for anything with a motor or compressor. A fridge that runs at 150 W can need 1,000 W or more for the first moment of each start. If your power station's surge rating is too low, it will trip and shut off every time the compressor kicks in. Sump pumps, air conditioners and furnace fans behave the same way.

What about mAh?

Power banks are often sold in milliamp-hours (mAh). That number leaves out the voltage, so you can't compare it directly with Wh. To convert:

Power banks almost always quote mAh at the battery's internal 3.7 V. So a "20,000 mAh" power bank is 20,000 × 3.7 ÷ 1,000 = 74 Wh, less than a tenth of a 1,000 Wh power station.

Wh is also the number airlines use. In the US, the FAA allows lithium batteries up to 100 Wh in carry-on bags, 101–160 Wh with airline approval, and nothing above 160 Wh. That rules out almost every power station.

Four buying mistakes

1. Buying on watts alone. A unit marketed as "2,000 W" might hold only 500 Wh. It can start your microwave, but it won't get you through a night.
2. Forgetting surge. The fridge only needs 150 W, so a 300 W unit should be fine, right? Not if the compressor needs 1,000 W to start.
3. Using the full rated capacity. Plan on about 85% of the Wh figure when you use the AC sockets.
4. Planning for heat. Space heaters and electric cooking empty even large units in an hour or two. For heat during an outage, look at other options and use the power station for the furnace fan, lights and fridge instead.

How we worked this out: run times are calculated from typical appliance ratings and an 85% usable-capacity assumption, not measured on specific products. Real results vary with temperature, battery age and the exact appliance.