Power Station Runtime Calculator

The starting point is one line: runtime (hours) = battery capacity (Wh) ÷ device power draw (W). A 1,000 Wh power station running a 100-watt device works out to roughly 10 hours on paper. Halve the wattage and the runtime doubles; double the wattage and it halves.

That version is useful for a quick gut check, but it quietly assumes every watt-hour in the battery reaches your device. In practice you divide usable capacity by the device's average draw: runtime = (capacity × inverter efficiency × usable fraction) ÷ average watts. The usable fraction is 1 minus whatever reserve you keep — a 20% reserve leaves 0.8. The calculator above applies both adjustments for you once you enter a capacity, wattage, efficiency, and reserve percentage.

Several real-world factors pull actual runtime below the simple capacity-divided-by-watts number:

• Inverter conversion loss. Turning stored DC energy into household AC is typically 80 to 90% efficient. The rest leaves as heat, so an AC device effectively sees only that fraction of the battery.
• Battery reserve. Running a lithium battery to 0% every cycle shortens its life and leaves no buffer, so most people keep 10 to 20% unused. That reserve is capacity you paid for but deliberately don't spend.
• Standby and idle draw. The inverter, display, fans, and Bluetooth or Wi-Fi radios all consume a few watts whenever the unit is on, even with nothing plugged in.
• Temperature. Cold weather reduces the energy a battery can deliver, and high loads that run the cooling fans hard add their own overhead.
• Battery age. Usable capacity slowly declines over hundreds of cycles, so a unit several years old won't match its original spec.
• Fluctuating and surge loads. Devices with motors or heating elements draw in bursts and spike well above their rated watts at startup, which the steady-average formula can't capture.

A reasonable rule of thumb is that real runtime lands somewhere around 80 to 90% of the naive figure for a steady electronic load, and less for motor- or heat-driven devices. The calculator above builds the two largest factors — efficiency and reserve — directly into its estimate.

The watt-hour number on the box is the rated capacity — the energy in the cells when full. What actually reaches your devices is smaller. Subtract inverter conversion loss, any reserve you choose to keep, and a little standby overhead, and a 1,000 Wh power station commonly delivers somewhere around 650 to 800 Wh of real AC output.

Enter capacity in the calculator as the rated figure and let the efficiency and reserve fields scale it down, or enter a measured usable figure directly and set efficiency to 100% with a 0% reserve. Some manufacturers publish a separate "usable capacity" or a real-world runtime chart for a given load — those are worth checking against your own estimate.

Battery chemistry matters at the margins too: lithium iron phosphate (LiFePO₄) packs tolerate deeper discharges and far more cycles than older lithium-ion designs, so owners often run them with a smaller reserve.

Runtime is only as accurate as the wattage you feed it, and the number printed on a device is often its maximum rather than what it actually uses. A few ways to get closer to the real figure:

• Plug-in watt meter. The most reliable option for AC devices — it shows live watts and accumulates watt-hours over time, which averages out any cycling.
• The label or manual. Look for a watts rating, or estimate it from volts × amps. Treat this as an upper bound for motor and heating appliances.
• Energy-guide figures. If a device lists an annual or daily kWh consumption, dividing that back down to an average wattage is usually more accurate than a nameplate number.
• Account for duty cycle. Refrigerators, freezers, and thermostatically controlled devices only run part of the time. Enter their average draw, or their running watts for the fraction of the hour they're actually on.

If your device can run on DC directly — many fridges, fans, and CPAP machines can — powering it from a 12V outlet skips the inverter and its conversion loss, which stretches runtime compared with the same device on an AC outlet.

A 500 Wh power station holds roughly 340 to 400 Wh of usable AC energy. That's about a full night for a CPAP without a humidifier, most of a workday for a laptop and phone, or several hours for a small TV. It generally isn't enough for a full-size refrigerator overnight.

A 1,000 Wh power station delivers around 680 to 800 Wh usable — one to two CPAP nights, a full day of light electronics, or roughly half a day to a day of a mini fridge depending on its cycling.

A 2,000 Wh power station gives roughly 1,350 to 1,600 Wh usable, which stretches to multiple days for low-wattage devices or about a day of a full-size refrigerator. High-wattage appliances — space heaters, kettles, hair dryers, air conditioners — still only run for tens of minutes to a couple of hours regardless of the size class, because their draw is measured in the hundreds or thousands of watts.

These are starting points. Enter the specific capacity and wattage into the calculator above for a figure that reflects your own hardware and settings.

When more than one device is plugged in, add their average wattages together and divide usable capacity by that combined figure. A 60-watt fridge plus a 12-watt router plus a 20-watt fan is a 92-watt load, so a 1,000 Wh power station with about 700 Wh usable lasts roughly seven to eight hours rather than the longer time any one device would get alone.

To estimate a mixed load without doing the arithmetic by hand, open the Power Station Size Calculator on the homepage, add every device with its wattage and hours, and use the built-in runtime estimator. It totals the watt-hours and applies the same efficiency and reserve settings shown here.

• Recharge with solar. A panel that keeps up with your daily consumption effectively removes the runtime limit for as long as the sun cooperates. Sustained multi-day use comes down to whether daily solar input matches daily draw — the Solar Charge Time Calculator estimates how long a panel needs to refill the battery.
• Run devices on DC. Powering a fridge, fan, or CPAP from a 12V outlet skips the inverter and recovers the 10 to 20% lost to AC conversion.
• Use eco or power-saving mode. Many units drop the AC output or auto-shut-off when the load is tiny, cutting idle drain.
• Lower the load. Dim a screen, lower a heater's setpoint, or swap an incandescent lamp for LED — runtime scales inversely with watts.
• Keep the battery moderate in temperature. A cold pack delivers less energy; extreme heat runs the fans harder. Room temperature is the sweet spot.
• Reduce your reserve carefully. Spending more of the battery buys runtime at the cost of long-term battery health — reasonable in a genuine emergency, less so as a daily habit.

If you're sizing rather than stretching, the Power Station Size Calculator works the problem in the other direction — from the runtime you need to the capacity to buy. Device-specific guides are also available for refrigerators, CPAP machines, and Starlink.