Power Station Run Time Calculator: How Long Will It Last?

This calculator estimates how long a portable power station will run a given load, based on its battery capacity, the wattage of the devices you plug in, and typical inverter efficiency. Enter your power station’s capacity in watt-hours (Wh), the total running watts of your devices, and the calculator returns the estimated run time in hours and minutes.

Formula

Run time (hours) = (Battery capacity in Wh × Inverter efficiency %) ÷ Load in watts

Where:

• Battery capacity (Wh) – the total energy stored in the battery, usually printed on the unit or in the manual. 1 Wh = 1 watt of power for 1 hour.
• Inverter efficiency (%) – the portion of battery energy that actually reaches your devices. Most portable power stations have efficiencies between 80% and 90%.
• Load (W) – the combined running wattage of everything you plug in. This is the steady power draw, not the startup surge.

Worked Example

Using the default values: a 1000 Wh power station, a 100 W load, and 85% efficiency.

1. First, multiply capacity by efficiency: 1000 Wh × 0.85 = 850 Wh of usable energy.
2. Then divide by the load: 850 Wh ÷ 100 W = 8.5 hours.
3. In minutes: 8.5 × 60 = 510 minutes.

The calculator shows 8.50 hours and 510 minutes, matching the manual calculation.

How to Use This Calculator

Start by finding the battery capacity in watt-hours. It is usually listed on the side of the unit, in the spec sheet, or on the product page. If you only see amp-hours (Ah), multiply by the battery voltage (e.g., 12V × 50Ah = 600 Wh).

Next, determine the total load. Add up the running watts of every device you plan to power simultaneously. For example, a laptop (60 W), a LED lamp (10 W), and a phone charger (15 W) together draw 85 W. Use that number in the calculator.

Finally, set the inverter efficiency. Most modern power stations are 80–90% efficient. If you don’t know the exact figure, 85% is a reasonable default. Pure sine wave inverters tend to be at the higher end; modified sine wave units may be lower.

Factors That Affect Real Run Time

The formula gives an ideal estimate, but real-world run time can differ for several reasons:

• Battery age and temperature: Cold batteries deliver less usable energy; hot batteries degrade faster. A battery at 0°C may provide only 70–80% of its rated capacity.
• Startup surge: Devices like refrigerators and power tools draw 2–3 times their running wattage for a few seconds. This doesn’t change total run time much, but it can trip the inverter if the surge exceeds its peak rating.
• Idle draw: The power station itself consumes a small amount of power (5–15 W) just to keep the inverter and display on. For long run times, this can add up.
• Battery management system (BMS): The BMS may cut off power before the battery is fully drained to protect it, especially under high load.

How to Choose the Right Power Station

Use the calculator backward to size a power station. Decide how long you want to run your devices, then multiply the load by the hours. For example, to run a 100 W device for 10 hours, you need 1000 Wh of usable energy. With 85% efficiency, that means a battery capacity of about 1176 Wh (1000 ÷ 0.85).

Also consider the inverter’s continuous and peak wattage. The continuous rating must exceed your total running watts, and the peak rating must handle the largest startup surge. If you plan to run a 700 W microwave (which can surge to 1000 W), a 500 W inverter won’t work even if the run time math looks fine.

Finally, think about recharging options. Solar input, AC wall charging, and car charging all affect whether the unit can be replenished during an outage or off-grid trip. A larger battery is not always better if you can’t recharge it in a reasonable time.

Common Mistakes and Misconceptions

Mistake 1: Confusing watts with watt-hours. Watts measure power (how fast energy is used), watt-hours measure energy (how much is stored). A 500 W device running for 2 hours consumes 1000 Wh, not 500 Wh.

Mistake 2: Using peak watts instead of running watts. A refrigerator might surge to 800 W but only run at 150 W. Use the running wattage for run time calculations, but ensure the inverter can handle the surge.

Mistake 3: Ignoring inverter efficiency. Many people simply divide capacity by load, getting an optimistic result. A 1000 Wh battery with a 100 W load gives 10 hours in theory, but only 8.5 hours at 85% efficiency.

Mistake 4: Assuming the rated capacity is fully usable. Most lithium batteries are designed not to discharge below 10–20% to extend lifespan. Some power stations reserve that automatically, so usable capacity is less than rated.

Run Time Comparisons by Device

Here are typical run times for a 1000 Wh power station at 85% efficiency (usable 850 Wh):

• LED light bulb (10 W) – 85 hours
• Laptop (60 W) – 14.2 hours
• Mini fridge (80 W) – 10.6 hours
• CPAP machine (100 W) – 8.5 hours
• Electric blanket (150 W) – 5.7 hours
• TV (120 W) – 7.1 hours

These are estimates. Check the actual wattage on each device’s label or with a plug-in watt meter for more accuracy.

Safety Considerations

Never exceed the power station’s rated output. Overloading the inverter can cause overheating, tripped breakers, or damage to the unit and connected devices. Use the calculator to stay within the continuous wattage limit.

Keep the power station in a dry, ventilated area. Do not cover it while running, as it generates heat. Follow the manufacturer’s instructions for charging and storage, and avoid exposing the battery to extreme temperatures.

If you are using the power station for medical devices, always have a backup plan. Battery run time can vary unexpectedly, so test your equipment under real conditions before relying on it.

Alternatives to a Single Power Station

If your run time needs are high, consider these options:

• Multiple power stations: Run different devices on separate units to balance the load and extend total run time.
• Solar generators: Pair a power station with solar panels to recharge during the day, effectively extending run time indefinitely in sunny conditions.
• Gas or propane generators: For very high loads or long outages, a fuel generator may be more practical, though it adds noise, fumes, and fuel costs.
• Battery packs with DC output: If your devices run on 12V DC (like car accessories), using the DC port avoids inverter losses and increases efficiency.

Frequently Asked Questions

How do I convert amp-hours (Ah) to watt-hours (Wh)?

Multiply the amp-hour rating by the battery voltage. For example, a 12V battery rated at 50Ah has 12 × 50 = 600 Wh. Most power stations list capacity in Wh, but if you only see Ah, this conversion is essential.

Why does my actual run time differ from the calculator?

Real-world factors include battery age, temperature, inverter efficiency, idle draw, and the fact that the battery management system may reserve some capacity. The calculator gives an ideal estimate; expect 80–90% of that in practice, especially in cold conditions or with older batteries.

Can I run a refrigerator with a power station?

Yes, if the power station’s continuous wattage exceeds the fridge’s running watts and its peak wattage handles the startup surge. A typical mini fridge draws 50–100 W running, but can surge to 200–300 W. Use the running watts for run time, but check the surge rating.

What does inverter efficiency mean?

It’s the percentage of battery energy converted to AC power that reaches your devices. The rest is lost as heat. Most power stations are 80–90% efficient. Using DC output (if available) bypasses the inverter and improves efficiency.

Is it safe to run a power station at full load?

It’s generally safe, but running at maximum continuously can reduce battery lifespan and cause the unit to heat up. The calculator will show a shorter run time at full load, which is expected. Always ensure the load does not exceed the inverter’s continuous rating.

How long does a 500Wh power station run a 100W device?

At 85% efficiency, usable energy is 425 Wh. Divide by 100 W gives 4.25 hours. The same calculation applies to any capacity and load.

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in cap | Battery capacity | Wh | 1000 | 0 | 100000
in load | Total device load | W | 100 | 0 | 10000
in eff | Inverter efficiency | % | 85 | 50 | 99
out run_h | Estimated run time | h | cap * eff / 100 / load | 2
out run_min | Run time (min) | min | cap * eff / 100 / load * 60 | 0