A portable power station can run a phone for days or a refrigerator for only a few hours, depending on its watt-hour capacity, inverter efficiency, device load, and duty cycle. This guide provides a reusable portable power station runtime chart, simple formulas, and worked examples so you can estimate how long a solar battery will run your devices before camping, traveling, or preparing for an outage.
Overview
The most useful specification for estimating runtime is a power station’s battery capacity, measured in watt-hours (Wh). Watt-hours describe how much energy the battery stores. A device’s power demand is measured in watts (W). In its simplest form, runtime is calculated by dividing available watt-hours by the device’s wattage.
For example, a 500 Wh power station connected to a 50 W device appears to provide 10 hours of runtime. In practice, the result will be lower because the inverter uses energy, the battery may not be fully discharged, and the device may not draw a constant load. A more realistic estimate accounts for usable battery capacity and conversion losses.
Use this basic formula:
Estimated runtime in hours = battery capacity in Wh × usable-capacity factor × inverter-efficiency factor ÷ device load in W
For an AC appliance, a practical starting assumption is a usable-capacity factor of 0.85 and an inverter-efficiency factor of 0.90. These are planning assumptions, not guarantees. Check the power station manual for its recommended depth of discharge, efficiency information, low-battery shutdown behavior, and output limits.
Portable power station runtime chart
The chart below uses a 500 Wh battery, 85% usable capacity, and 90% inverter efficiency. The estimated usable AC energy is therefore about 383 Wh. Actual results vary by model and appliance.
| Device or load | Example running load | Approximate runtime from 500 Wh |
|---|---|---|
| LED light | 10 W | About 38 hours |
| Phone charger | 10–15 W while charging | About 25–38 hours of active charging |
| Laptop | 45 W | About 8.5 hours |
| CPAP machine | 40–60 W, depending on settings | About 6–9.5 hours |
| Small fan | 40 W | About 9.5 hours |
| Mini refrigerator while running | 60 W | About 6.4 hours of equivalent run time |
| Television | 100 W | About 3.8 hours |
| Small microwave | 1,000 W | About 23 minutes of equivalent runtime |
“Equivalent runtime” matters for appliances that cycle on and off. A refrigerator may draw power for only part of each hour, so its elapsed backup time can be longer than the continuous-runtime figure suggests. Temperature, ventilation, door openings, age, and the appliance’s control settings all affect the result.
How to estimate runtime
- Find the battery capacity. Look for the power station’s rated capacity in Wh. Do not confuse watt-hours with the unit’s maximum output in watts. A station may store 1,000 Wh but still be unable to operate an appliance requiring more than its inverter’s continuous rating.
- Identify the actual device load. Read the appliance label, charger, manual, or manufacturer specification. A label may show volts and amps instead of watts. Multiply volts by amps to estimate watts: W = V × A. For USB devices, the charger’s maximum rating may be higher than the device’s average draw.
- Account for usable energy. Multiply rated capacity by a usable-capacity factor. A factor between 0.80 and 0.90 is a reasonable planning range when exact product data is unavailable, but the manufacturer’s specifications should take priority.
- Account for conversion losses. AC devices use the station’s inverter, while USB and DC outputs may use a different conversion path. Apply an efficiency factor appropriate to the output being used. If you do not know it, use a conservative assumption rather than treating rated Wh as fully available.
- Check startup demand. Motors and compressors can draw a brief surge when starting. Refrigerators, pumps, fans, and some power tools may need more starting watts than their running-watt figure. Compare both the device’s starting requirement and running requirement with the power station’s surge and continuous ratings.
- Combine loads carefully. Add the running watts of all devices operating at the same time, then use that total in the formula. Also verify that the combined demand remains below the station’s output limit.
For a DC or USB device, use the same general method, but avoid automatically applying an AC inverter loss if the device is powered directly from a DC output. The product manual may provide separate runtime guidance for each port.
Inputs and assumptions
Runtime estimates are only as good as their inputs. Before choosing a portable solar battery, record the following:
- Battery capacity: rated Wh, not just the model name or battery voltage.
- Device wattage: running watts under the conditions in which you expect to use the device.
- Duty cycle: whether the appliance runs continuously or cycles on and off.
- Output type: AC, USB, or DC. Direct DC operation can avoid some inverter losses.
- Startup surge: especially important for refrigerators, pumps, compressors, and motor-driven equipment.
- Temperature: very hot or cold conditions may affect battery performance and operating limits.
- Battery age and condition: capacity can decline with use, storage conditions, and time.
When the exact wattage is unknown, a plug-in watt meter can measure many AC appliances. Measure the appliance while it is performing its normal task, not only when idle. For a refrigerator, observe it long enough to capture compressor starts and cycling. Do not rely on a single low reading for a device with a variable load.
Solar input changes the calculation. A connected portable solar panel can extend runtime or recharge the battery during the day, but panel ratings represent test conditions rather than guaranteed household output. Shade, orientation, clouds, temperature, cable losses, charge limits, and the station’s maximum solar-input rating all matter. Treat solar charging as a separate energy input: estimated daily solar energy is panel wattage multiplied by effective sun hours, then reduced for real-world losses.
Worked examples
Example 1: laptop and lights
Suppose a 500 Wh power station runs a 45 W laptop and two 10 W lights. The combined load is 65 W. Using 383 Wh of estimated usable AC energy:
383 Wh ÷ 65 W = about 5.9 hours
If the laptop is not charging continuously, or the lights are switched off periodically, the elapsed time may be longer. If the laptop is powered through USB-C rather than an AC charger, the result may also differ because the power path changes.
Example 2: refrigerator backup
Assume a refrigerator draws 120 W while its compressor is running, but operates for an estimated 40% of the time. Its average load would be approximately 48 W. Using the same 383 Wh usable energy:
383 Wh ÷ 48 W = about 8 hours of estimated elapsed runtime
This is not a guarantee. The refrigerator may need a substantially higher starting surge, and its duty cycle can increase in a warm room or when the door is opened frequently. Confirm the power station’s surge rating before relying on it for food preservation.
Example 3: CPAP machine
A CPAP machine may use different amounts of energy depending on pressure, humidification, heated tubing, and the manufacturer’s power adapter. If the measured average load is 50 W, the same 500 Wh station provides:
383 Wh ÷ 50 W = about 7.7 hours
For overnight use, measure the complete setup and include accessories. Heated humidifiers and heated tubing can materially change consumption. Anyone depending on a CPAP device should follow the equipment manufacturer’s backup-power guidance and test the setup before an outage or trip.
When to recalculate
Recalculate runtime whenever a major input changes. This includes buying a different power station, adding a refrigerator or medical device, changing from AC to USB or DC output, or connecting portable solar panels. Recheck the estimate when battery capacity has declined, the appliance is moved to a hotter or colder environment, or you begin using features such as refrigerator ice makers, CPAP humidifiers, or laptop docking stations.
It is also worth testing your setup before a camping trip or emergency. Fully charge the station, connect the intended devices, record the starting battery percentage, and observe the load over several hours. This practical test can reveal startup problems, unexpected standby consumption, overloaded outlets, or a shorter-than-expected runtime.
For larger planning decisions, pair this worksheet with a solar battery size calculator or the solar panel system sizing guide. If you are assembling a broader solar panel kit, confirm that the panels, charge controller, cables, inverter, and battery are electrically compatible. Keep the final estimate conservative, leave reserve capacity for unexpected loads, and never exceed the power station’s stated voltage, current, continuous-watt, or surge limits.
