Battery Life Calculator
70% is recommended to prevent deep discharge.
Time = (Cap × Efficiency) / Consumption
Estimate the runtime of your batteries with precision. Our Battery Life Calculator accounts for capacity, power draw, and efficiency margins to give you a realistic expectation of how long your devices will last before needing a recharge.
Looking for a quick answer? A standard 2000mAh battery powering a 100mA device will last roughly 14 hours when following the 70% efficiency rule. Use the tool above to customize your specific hardware parameters.
- Calculates for mAh, Ah, and Watts
- Includes safety/efficiency margin slider
- 100% free for electronics and DIY projects
Introduction to Battery Life
Battery life is one of the most critical specifications for portable electronics, solar storage systems, and electric vehicles. It represents the duration a battery can supply power to a specific load before its voltage drops below the functional threshold. Understanding how to calculate this runtime allows engineers and hobbyists to size their power sources correctly.
While the basic math seems simple—dividing capacity by consumption—the physical reality of battery chemistry introduces variables like internal resistance and discharge curves. This tool helps bridge the gap between "perfect" math and real-world performance by incorporating efficiency factors.
How to Use the Battery Life Calculator
Follow these steps to get an accurate estimation for your device:
- Enter Battery Capacity: Input the total capacity of your battery. Common units are mAh (milliamp-hours) for small electronics and Ah (Amp-hours) for larger lead-acid or lithium banks.
- Input Device Consumption: Enter how much current your device draws. If you only know the wattage, select 'Watts' from the dropdown and provide the system voltage.
- Adjust Efficiency: Batteries rarely provide 100% of their rated capacity. We recommend 70% for a conservative, safe estimate that preserves battery health.
- Review Results: The calculator instantly displays the runtime in hours and minutes, as well as the total usable capacity in the chosen unit.
How the Calculation Works
The core formula used by our calculator is the standard discharge equation, modified by an efficiency coefficient:
Runtime (Hours) = (Capacity × Efficiency) / Load Current When you enter power in Watts, we first convert it to Amps using Ohm's Law (Amps = Watts / Volts). This ensures that the consumption units match the capacity units for a mathematically sound result.
Key Factors That Affect Battery Performance
- Peukert's Effect: As the discharge rate increases, the available capacity of the battery decreases. This is especially prominent in lead-acid batteries.
- Temperature: Batteries are chemical devices. Extreme cold increases internal resistance, while extreme heat can lead to faster degradation and reduced capacity.
- Age: Batteries lose capacity over time through a process called sulfation or lithium plating, depending on the chemistry.
- Discharge Depth: Discharging a battery to 0% often causes permanent damage. This is why we include the efficiency/safety margin by default.
Assumptions and Limitations
This calculator provides a theoretical estimate based on several assumptions:
- Constant Load: It assumes the device draws the exact same amount of power throughout the entire discharge cycle.
- Healthy Battery: It assumes the battery is relatively new and meets its manufacturer-rated capacity.
- Nominal Voltage: For Watt-based calculations, it assumes the system voltage remains constant, which is not strictly true as a battery drains.
3 Practical Battery Life Examples
1. IoT Sensor
A small sensor using a 2400mAh AA battery and drawing 2mA constantly.
Efficiency: 85%
Runtime: 1,020 Hours
(~42 Days)
2. LED Flashlight
A high-power light using a 3500mAh 18650 cell drawing 1.5A.
Efficiency: 70%
Runtime: 1.6 Hours
(~1h 38m)
3. Solar Battery Bank
A 100Ah 12V marine battery powering a 60W portable fridge.
Efficiency: 50% (Lead-acid safe)
Runtime: 10 Hours
(60W / 12V = 5A load)
Quick Reference Table
Common battery sizes and estimated runtimes at a standard 100mA load (using 70% efficiency).
| Battery Type | Typical Capacity | Runtime (100mA) | Runtime (500mA) |
|---|---|---|---|
| AAA (Alkaline) | 1,000 mAh | 7 Hours | 1.4 Hours |
| AA (Alkaline) | 2,500 mAh | 17.5 Hours | 3.5 Hours |
| 9V (Alkaline) | 500 mAh | 3.5 Hours | 0.7 Hours |
| 18650 (Lithium) | 3,400 mAh | 23.8 Hours | 4.7 Hours |
Frequently Asked Questions
What does mAh stand for?
mAh stands for milliamp-hour. It is a unit of electric charge, indicating how much current (in milliamps) a battery can supply for one hour.
How do I convert Watts to Amps?
To convert Watts to Amps, divide the Power (Watts) by the Voltage (Volts). For example, a 12W light on a 12V battery draws 1 Amp.
Should I discharge my battery to 0%?
No. Most modern batteries (Lithium, Lead-Acid) suffer damage when fully depleted. Staying above 20-30% capacity significantly extends the battery's lifespan.
Conclusion
Calculating battery life is essential for reliable device design and power management. By understanding the relationship between capacity, consumption, and efficiency, you can ensure your projects never run out of juice unexpectedly. Whether you're building a remote sensor or sizing a solar battery bank, our calculator provides the realistic estimations you need to power your ideas.