The calculation is theoretically accurate based on the inputs provided, but real-world conditions can affect actual runtime. Factors like temperature, battery age, and actual device power draw (which may vary based on usage) can cause variations. Our calculator accounts for typical efficiency losses (85% by default), but for critical applications, we recommend testing your actual setup.

Battery capacity in mAh alone doesn't tell the full story because different batteries operate at different voltages. To calculate total energy (watt-hours), we need both mAh and voltage (V). Similarly, device power in watts is calculated as amps × volts. This allows us to compare battery capacity and device power consumption in consistent units (watt-hours and watts).

Most quality power banks have efficiency between 80-90%. The default 85% in our calculator is a good average. Lower-quality power banks might be less efficient (70-80%), while premium models with advanced circuitry can reach 90-93%. If you're unsure, check your power bank's specifications or run tests comparing its rated capacity to actual output.

Our calculator currently handles one device at a time. For multiple devices, you have two options: 1) Calculate runtime for each device separately (if they'll be used one at a time), or 2) Add up the power consumption of all devices that will run simultaneously and enter the total wattage. Remember that running multiple devices at once will drain your battery faster.

Check your device's label, manual, or specifications sheet for power requirements. Look for values in watts (W) or amps (A). If only amps are listed, you'll need the operating voltage to calculate watts (W = A × V). For devices with variable power (like laptops), use the average or maximum power draw. Our blog has a detailed guide on finding power consumption for different device types.

Several factors can cause this: 1) Your device's actual power draw may be higher than rated (especially under heavy use), 2) Battery capacity may degrade over time, 3) Environmental factors like cold temperatures reduce battery performance, 4) The efficiency percentage may need adjustment (try lowering it), or 5) There may be parasitic drains from connected but unused devices.

Yes, the same principles apply to any DC power system. For car batteries, use the battery's amp-hour (Ah) rating and 12V (or 24V for some systems). For solar, you'd calculate based on your battery bank's capacity. Note that lead-acid batteries typically shouldn't be discharged below 50%, so you'd only calculate with half their rated capacity.

Different battery chemistries have varying characteristics: Lithium-ion (common in power banks) maintains relatively stable voltage until nearly depleted, providing consistent power. Lead-acid batteries voltage drops gradually under load. Nickel-based batteries have different discharge curves. Our calculator assumes lithium-ion behavior, which is most common for portable applications.

Yes, lithium-ion batteries typically lose about 20% of their capacity after 300-500 full charge cycles. If your power bank is older or heavily used, you might reduce the capacity value by 10-30% to account for this. Some premium power banks display remaining capacity percentage, which you could use directly in the calculator.

Currently, our calculator doesn't have a save feature, but you can bookmark the page with your inputs (they remain in the URL), take a screenshot, or note down the results. We're working on adding account features for saving calculations and creating power plans for different scenarios.