How Long Will a Power Station Last?

Power station runtime is not mysterious, but it is easy to misjudge because the battery number on the box is not the same as the energy you actually get at the plug. Once you correct for that, the maths becomes simple.

The core question is always the same: how many usable watt-hours does the battery deliver, and how many watts is your setup drawing?

Quick Answer

• 720 usable Wh / 60W = about 12 hours
• 720 usable Wh / 90W = about 8 hours
• 720 usable Wh / 200W = about 3.6 hours
• Runtime falls directly as load rises

The simple formula is: runtime (hours) = usable Wh / device watts.

The part people usually miss is the “usable” bit. For AC loads, the real number is often around 70 to 75% of the rated battery capacity. For more on that, see You Only Get Half the Battery.

Common Runtime Examples on a 1000Wh-Class Station

Load	Typical watts	Runtime on ~720 usable Wh
Router	12W	~60 hrs
CPAP	40W	~18 hrs
Laptop	60W	~12 hrs
Fridge (average)	70W	~10 hrs
Desktop + monitor	200W	~3.6 hrs

Darker cells mean longer runtime. These assume moderate conditions and AC output use.

Why the Real Number Is Lower

Cause	Effect on runtime
Inverter losses	Converting DC battery power into AC wastes part of the stored energy.
Battery reserve and protection	The battery management system usually keeps a little energy inaccessible.
Temperature	Cold conditions often reduce the energy you can actually use.
Heavy or uneven loads	Real-world behaviour is rarely as clean as the label maths.

If you want the distinction between watts and watt-hours cleaned up first, read What Are Watt-Hours? A Simple Explanation. If the load includes a compressor, also check What Is Startup Surge?.

Try It in the Calculator

Setup	Scenario	Open
Laptop	8 hours	Calculate
CPAP	8 hours	Calculate
Small fridge	8 hours	Calculate
Laptop + router + lamp	8 hours	Calculate

If you want the exact result for your own device mix, use the calculator. It is faster and safer than doing the full correction by hand.

What People Miss

Load matters more than battery label. A small change in watts can cut runtime dramatically.

AC and DC use do not behave identically. USB and 12V outputs usually waste less than AC sockets.

Fridges are not steady loads. Their average draw can be moderate, but surge still matters for startup.

Usable energy beats rated energy. Marketing numbers are not runtime numbers.

Bottom Line

To estimate how long a power station lasts, divide usable watt-hours by the real average watts of your setup. That is the clean answer. Everything else is about getting the usable number and the load number right.

If you want to skip that work, try this in the calculator and let it do the corrections for efficiency, surge, and safety margin automatically.