mAh, Wh & Runtime Calculator
Estimate battery energy and expected runtime from your battery specs and device power draw.
Tip: For power banks, using 80–90% efficiency is usually realistic.
What Is mAh and Why It Matters
mAh stands for milliamp-hours. It is a battery capacity unit that tells you how much charge a battery can deliver over time. A higher mAh number generally means longer battery life, but only if voltage and power demand are similar.
For example, a 5,000 mAh battery can theoretically deliver 5,000 milliamps for one hour, or 500 milliamps for ten hours. Real-world results are always lower because of heat loss, conversion loss, age, temperature, and usage patterns.
mAh vs Ah vs Wh: Quick Comparison
1) mAh (milliamp-hours)
Best for comparing small batteries and consumer devices like phones, earbuds, and handheld gadgets.
2) Ah (amp-hours)
Just a larger unit: 1 Ah = 1000 mAh. Common in larger battery systems like solar or automotive setups.
3) Wh (watt-hours)
Watt-hours represent total energy and include voltage, so Wh is often a better comparison across different battery types.
- Ah = mAh / 1000
- Wh = (mAh / 1000) × Voltage
How This mAh Calculator Works
This calculator estimates how long your battery can run a device based on five inputs:
- Battery Capacity (mAh): total stated battery capacity.
- Voltage (V): battery nominal voltage.
- Current Draw (mA): average load current of your device.
- System Efficiency (%): losses from regulators/boost converters/cables.
- Usable Capacity (%): how much of rated capacity is actually usable.
Runtime is estimated with: Runtime (hours) = (mAh × Efficiency × Usable Capacity) ÷ Current Draw
Example: 10,000 mAh battery, 500 mA load, 85% efficiency, 100% usable capacity: runtime ≈ (10,000 × 0.85 × 1.00) / 500 = 17 hours.
Practical Examples
Phone Charging from a Power Bank
A 10,000 mAh power bank is rated internally at about 3.7V. Your phone charges at around 5V, so conversion losses occur. That is why a 10,000 mAh bank rarely gives a full 10,000 mAh at USB output.
Battery-Driven IoT Sensor
If your sensor averages 120 mA and your battery is 2,400 mAh with 90% effective usable output, runtime is: (2400 × 0.90) / 120 = 18 hours.
Portable LED Light
Suppose a light uses 700 mA continuously. A 6,000 mAh battery with 85% total usable output gives: (6000 × 0.85) / 700 ≈ 7.3 hours.
Common Battery Calculation Mistakes
- Ignoring voltage: Same mAh at different voltages means different energy.
- Assuming 100% efficiency: Real systems lose energy during conversion.
- Using peak current instead of average current: runtime estimates become inaccurate.
- Forgetting aging effects: older batteries can lose 10–30% capacity.
- Neglecting temperature: cold environments reduce available capacity significantly.
Tips to Improve Battery Runtime in Real Devices
Lower Average Current Draw
Use low-power modes, dim displays, reduce wireless transmit intervals, and optimize firmware loops.
Improve Conversion Efficiency
Choose quality regulators and avoid unnecessary voltage conversion stages when possible.
Use Conservative Planning Margins
For reliable design, target only 70–85% of rated battery capacity depending on environment and required uptime confidence.
Frequently Asked Questions
Is a higher mAh battery always better?
Not always. Higher capacity usually means larger size, more weight, and longer charge time.
Can I compare two batteries by mAh alone?
No. Compare watt-hours (Wh) when voltages differ.
Why does my real runtime differ from the estimate?
Device load changes constantly, and efficiency is not fixed at all loads. Battery condition, temperature, and protection cutoffs also affect results.
Final Takeaway
A good mAh calculator turns battery labels into meaningful runtime expectations. If you include voltage, realistic efficiency, and average current draw, your estimate becomes much closer to real-world behavior. Use the calculator above before buying batteries, sizing power banks, or planning portable projects.