calculate run time of battery and Estimate how long a battery will last based on its capacity (Ah/mAh), voltage (V), and the average power consumption (W) of the device it powers.
Battery Runtime Calculator
Estimate the operational time for your device based on battery specifications and power consumption. Enter the details below.
Disclaimer: This calculation provides an **estimate only**. Actual battery runtime can be significantly affected by battery age/health, discharge rate, temperature, device power fluctuations, and battery cut-off voltage.
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How Battery Runtime is Estimated
This calculator estimates the battery life based on fundamental electrical principles:
- Calculate Battery Energy (Watt-hours): First, the total energy stored in the battery is calculated. Energy (in Watt-hours, Wh) is found by multiplying the battery's charge capacity (in Ampere-hours, Ah) by its nominal voltage (V). If capacity is given in mAh, it's converted to Ah first (mAh / 1000 = Ah).
Energy (Wh) = Capacity (Ah) × Voltage (V) - Calculate Runtime (Hours): The total stored energy (Wh) is then divided by the average rate at which the device consumes energy (Power in Watts, W).
Runtime (hours) = $\frac{\text{Battery Energy (Wh)}}{\text{Device Power (W)}}$
Key Units:
- Ah/mAh (Ampere-hours/milliampere-hours): Measures battery charge capacity – how much current a battery can provide over time.
- V (Volts): Measures electrical potential difference.
- Wh (Watt-hours): Measures energy storage, combining capacity and voltage. Often used for comparing batteries of different voltages.
- W (Watts): Measures power – the rate at which energy is used (Joules per second).
Important Factors Affecting Real Runtime:
The calculated runtime is theoretical. Real-world factors significantly impact actual battery life:
- Battery Health & Age: Capacity decreases as a battery ages and goes through charge cycles.
- Discharge Rate (Peukert's Effect): Batteries often provide less *effective* capacity when discharged quickly (high power draw) compared to slow discharge rates. This calculator uses the nominal capacity.
- Temperature: Extreme hot or cold temperatures reduce battery performance and longevity.
- Device Power Fluctuation: Devices rarely draw constant power. Peak draws (like screen brightness increase, CPU load) use more energy. The calculator uses the *average* power consumption.
- Cut-off Voltage: Devices stop operating before the battery voltage drops to absolute zero to protect the battery. Usable capacity is less than total capacity.
- Efficiency Losses: Power conversion within the device or battery management system isn't 100% efficient.
Therefore, use this result as a guideline or upper estimate.
Frequently Asked Questions (FAQs)
How do I find my device's power consumption in Watts?
Check the device's specifications (manual, label, manufacturer website). Sometimes it's listed in Watts (W). If listed in Amps (A) or milliamps (mA), you can estimate power using $P = I \times V$ (Power = Current × Voltage), using the device's operating voltage (often similar to the battery voltage for simple devices).
What's the difference between Ah/mAh and Wh?
Ah/mAh measures charge capacity (current over time). Wh measures energy (charge capacity * voltage). Wh is often better for comparing batteries with different voltages because it represents the total energy stored. This calculator calculates Wh as an intermediate step.
Why is my actual battery life shorter than the calculated estimate?
As listed in the 'Important Factors' section, real-world conditions like high power draw (Peukert's effect), battery age, temperature extremes, fluctuating device power needs, and the device's cut-off voltage all tend to reduce the actual runtime compared to this ideal calculation.
What is Peukert's Law?
Peukert's Law describes how the available capacity of a battery (especially lead-acid) decreases as the rate of discharge increases. Discharging a battery quickly yields less total energy than discharging it slowly. This calculator does not account for Peukert's Law.
Can I calculate runtime if I only know the current draw (Amps)?
Yes, if you also know the voltage. First, calculate Power (Watts) = Current (Amps) × Voltage (Volts). Then use that Power value in this calculator along with the battery capacity and voltage.
