Calculate Battery Runtime & Device Battery Life
See step-by-step calculation
Battery capacity and power consumption are critical for understanding device runtime. Whether you're designing electronics, managing IoT power systems, or curious about your phone or laptop battery life, calculating runtime from mAh capacity and mA current draw is essential. This free tool applies the standard formula for accurate estimates. Updated through 2026.
Battery capacity and power consumption are critical for understanding device runtime. Whether you're designing electronics, managing IoT power systems, or curious about your phone or laptop battery life, calculating runtime from mAh capacity and mA current draw is essential. This free tool applies the standard formula for accurate estimates. Updated through 2026.
When to use this calculator
- Electronics and IoT device design and power budgeting
- Estimating smartphone and laptop battery runtime
- Engineering and electronics students and professionals
- Portable device power management and optimization
- Battery selection for circuits and embedded projects
- Validating theoretical battery life before purchase decisions
Example Calculation
- 3000 mAh ÷ 200 mA
- 15 hours
How it works
1 min readBattery Runtime Fundamentals
Battery runtime is a core calculation in electronics and portable device design. By dividing a battery's capacity (measured in milliamp-hours, mAh) by a device's current draw (measured in milliamps, mA), you get the estimated runtime in hours.
How to Calculate
Enter your battery capacity and the device's average current consumption. The calculator applies the standard formula:
Runtime (hours) = Battery Capacity (mAh) ÷ Current Draw (mA)
This assumes constant power draw, which is a solid baseline for most portable devices and circuits.
Important Notes
This calculation is an estimate based on standard assumptions. Real-world battery life varies significantly due to temperature, battery age, usage patterns, and device efficiency. For critical applications or professional design decisions, consult with an electrical engineer or battery specialist. Values are accurate as of 2026.
Frequently asked questions
How long will my phone battery last with this calculator?
Find your battery capacity in phone settings and estimate average current draw. Light use: 100–150 mA, moderate use: 200–300 mA, gaming or video: 400+ mA. The result is theoretical maximum under constant load.
What's the difference between mAh and Wh?
Wh (watt-hours) = (mAh × Voltage) ÷ 1000. Wh is a more accurate measure of total energy stored, while mAh describes capacity at a specific voltage (usually 3.7V for lithium cells).
Why does my actual battery life fall short of this estimate?
Real devices have highly variable power draw. Idle consumption is much lower than active use. Screen brightness, cellular radios, Wi-Fi, GPS, and background apps all increase draw above the average.
How many charge cycles do lithium batteries last?
Most lithium batteries tolerate 300–1000 charge cycles (typically 500–800) before capacity drops to ~80%. This varies by chemistry, thermal conditions, and charging practices.
Does fast charging reduce battery lifespan?
Yes. Fast charging generates significant heat, which stresses battery chemistry. Charging between 20% and 80%, avoiding fast charging, and keeping devices cool extend lifespan dramatically.
How does temperature affect battery runtime and health?
Cold reduces runtime by 15–30% but doesn't cause permanent damage. Heat (above 95°F) accelerates degradation. Optimal performance is 68–72°F. Avoid freezing or overheating your device.
What's the best charge level for battery longevity?
Keeping charge between 20% and 80% significantly extends battery lifespan compared to 0–100% cycles. Many modern phones have optional battery health features that cap charging at 80%.
Is this calculator reliable for my device?
It's reliable for steady-state estimates under constant load. Real devices alternate between idle, moderate, and peak power draw. Use this as a theoretical maximum; expect actual runtime 20–40% shorter with mixed usage.