How Long Will a Power Station Last?

You just bought a portable power station — or you are thinking about buying one — and the first question on your mind is simple: how long will it actually keep my stuff running? The answer depends on a few factors, but the math is not complicated once you know what to look for.

The Basic Runtime Formula

At its core, the calculation is:

Runtime (hours) = Usable Wh / Device Watts

If a power station has 500 usable watt-hours and your device draws 100 watts, you get roughly 5 hours of runtime. Double the device wattage to 200W and the runtime drops to 2.5 hours. Halve it to 50W and you get 10 hours.

The tricky part is figuring out what “usable Wh” actually means, because it is not the same as the number on the box.

Rated Capacity vs. Usable Capacity

When a manufacturer says a power station has 1,000 Wh, they are describing the total energy stored in the battery cells under ideal lab conditions. In the real world, you will never get to use all of it. Energy is lost along the way, and several factors eat into your actual runtime.

Inverter Efficiency

If you are plugging in AC devices (anything with a standard wall plug), the power station must convert its stored DC energy to AC through an inverter. This conversion is not free. Most inverters operate at about 85% efficiency. For every 100 Wh the battery releases, only about 85 Wh make it to your device. The rest is lost as heat.

If you are powering DC devices directly — through USB ports or a 12V car-style outlet — you skip this loss entirely. This is one reason USB-powered devices get noticeably longer runtimes from the same battery.

Depth of Discharge

Most modern power stations use lithium-ion or LiFePO4 batteries. Their built-in battery management systems typically prevent the battery from being drained to absolute zero, reserving a small percentage to protect the cells. This means you might only access 90–95% of the rated capacity before the unit shuts off.

Temperature

Batteries perform best at moderate temperatures. In cold weather (below about 40F / 5C), a lithium-ion battery can lose 10–20% of its effective capacity. If you are using a power station in a cold garage or outdoors during winter, expect shorter runtimes than the spec sheet suggests.

The Combined Effect

When you stack these factors, a rough rule of thumb emerges:

Usable Wh is roughly 70–75% of rated Wh for AC loads under normal conditions.

A power station rated at 1,000 Wh will realistically deliver about 700–750 Wh to your AC devices. Plan around this number, not the headline spec.

Example Calculations

Let us run through a few common devices using a 1,000 Wh power station with an estimated 720 Wh of usable capacity.

Laptop

A typical laptop draws 50–90W depending on workload. At 60W (light work, screen at medium brightness):

720 Wh / 60W = 12 hours

That is a full workday on a single charge. Heavier workloads at 90W would bring it down to about 8 hours — still quite good.

CPAP Machine

A CPAP without a heated humidifier typically draws 30–60W. At 40W:

720 Wh / 40W = 18 hours

Plenty for two full nights of sleep. Turn on the heated humidifier and wattage can jump to 80–100W, cutting runtime in half. Many CPAP users traveling with a power station leave the humidifier off to stretch their battery life.

Refrigerator

This is where things get interesting. A full-size fridge might be rated at 150W, but its compressor does not run constantly. It cycles on and off, averaging around 60–80W over time. Using an average of 70W:

720 Wh / 70W = about 10 hours

That could get you through an overnight outage, but not much more. For longer outages, you will need a larger unit or a way to recharge (solar panels, for example).

Multiple Devices at Once

Running several devices simultaneously? Add their wattages together. A laptop at 60W, a router at 12W, and a lamp at 10W equals 82W total:

720 Wh / 82W = about 8.8 hours

The more devices you add, the faster the battery drains. Prioritize what you truly need during an outage.

Why Surge Wattage Matters

Some devices draw far more power when they first start up than when they are running steadily. This is called surge or startup wattage, and it is most common in anything with a compressor or motor — refrigerators, air conditioners, and some power tools.

A fridge might run at 150W but surge to 500–800W for a fraction of a second when the compressor kicks in. If your power station cannot handle that surge, it will shut down or throw an error, even if it has plenty of stored energy left.

When shopping for a power station, check two numbers:

• Continuous wattage: What it can deliver non-stop. Your running devices must stay below this.
• Surge wattage: What it can handle for brief spikes. Your highest-surge device must stay below this.

A power station rated at 1,000W continuous with 2,000W surge can handle a fridge that runs at 150W but surges to 800W. A smaller unit rated at 500W continuous with 1,000W surge would also work for the fridge. But a unit rated at 300W continuous with 600W surge would struggle.

Surge wattage does not affect your total runtime, but it determines which devices you can run at all.

Tips to Maximize Runtime

Run Fewer Devices

This sounds obvious, but it is the single most effective strategy. During an outage, decide what is essential. The router and a laptop are probably more important than a TV and a desk lamp.

Choose Energy-Efficient Devices

LED bulbs draw a fraction of what incandescent bulbs use. A modern laptop uses far less power than a desktop PC with a monitor. If you are buying devices specifically for backup use, energy efficiency directly translates to longer runtime.

Use DC When Possible

Powering devices through USB or 12V DC outputs avoids the inverter efficiency loss. If your laptop can charge over USB-C, use that instead of the AC outlet. You will gain roughly 15% more runtime from the same battery.

Factor In Charging Needs

If you plan to recharge the power station during an extended outage — via solar panels, a car, or a generator — your effective runtime extends well beyond a single charge. Many people pair a mid-size power station (500–1,000 Wh) with a portable solar panel to keep it topped up during multi-day outages.

Keep the Battery Warm

If you are using a power station in cold conditions, bring it indoors or insulate it. A warmer battery delivers more of its rated capacity.

Skip the Guesswork

Calculating runtime for a single device is simple enough. But when you are running multiple devices with different wattages, accounting for efficiency losses, and making sure you have enough surge headroom, the mental math gets messy.

Our calculator factors in efficiency losses and surge requirements to give you a safe runtime estimate. Add your devices, set how long you need them to run, and get product recommendations matched to your actual needs — no spreadsheet required.

Quick Reference

Device	Typical Watts	Runtime on 1,000 Wh (usable)
Laptop (light use)	60W	~12 hours
CPAP (no humidifier)	40W	~18 hours
Wi-Fi Router	12W	~60 hours
LED Lamp	10W	~72 hours
Fridge (average)	70W	~10 hours
Desktop PC + Monitor	200W	~3.6 hours

Remember, these estimates use roughly 720 usable Wh from a 1,000 Wh rated unit. Your actual results may vary based on your specific power station, device loads, and conditions. When in doubt, round your needs up and buy more capacity than you think you need.