mAh to Watt-Hours (Wh) Converter
Calculate battery capacity and energy by converting milliamp-hours (mAh) to watt-hours (Wh) with precise voltage input
Quick Conversion Examples
How to Convert mAh to Wh
Converting milliamp-hours to watt-hours requires knowledge of the battery voltage. This conversion is necessary because mAh measures electric charge while Wh measures energy capacity. The relationship between these units depends on voltage.
Conversion Formula:
Wh = (mAh × V) ÷ 1000
Where:
- Wh = Energy in watt-hours
- mAh = Electric charge in milliamp-hours
- V = Voltage in volts
Calculation Example
Problem: Convert a 5000 mAh battery at 3.7V to watt-hours
- Identify the values: Capacity = 5000 mAh, Voltage = 3.7V
- Apply the formula: Wh = (5000 × 3.7) ÷ 1000
- Multiply: 5000 × 3.7 = 18,500
- Divide by 1000: 18,500 ÷ 1000 = 18.5 Wh
Result: A 5000 mAh battery at 3.7V contains 18.5 Wh of energy
Common Battery Capacity Conversions
| Battery Type | Capacity (mAh) | Voltage (V) | Energy (Wh) |
|---|---|---|---|
| AA Alkaline | 2,700 | 1.5 | 4.05 |
| AAA Alkaline | 1,200 | 1.5 | 1.8 |
| AAAA Alkaline | 625 | 1.5 | 0.94 |
| C Alkaline | 8,000 | 1.5 | 12 |
| D Alkaline | 12,000 | 1.5 | 18 |
| 9V Alkaline | 565 | 9 | 5.09 |
| 18650 Li-ion | 2,500 | 3.6 | 9 |
| 18650 High Capacity | 3,500 | 3.6 | 12.6 |
| Smartphone Battery | 3,000 | 3.7 | 11.1 |
| Tablet Battery | 7,000 | 3.7 | 25.9 |
| Laptop Battery | 4,400 | 11.1 | 48.84 |
| Power Bank (10000mAh) | 10,000 | 3.7 | 37 |
Popular Conversion Scenarios
Smartphone Batteries
Modern smartphones typically use lithium-ion or lithium-polymer batteries rated at 3.7V or 3.8V. A phone with a 4000 mAh battery at 3.7V has 14.8 Wh of energy capacity, which determines how long the device runs between charges.
Power Banks
Power banks are marketed by their mAh rating, but the actual output capacity depends on voltage conversion. A 20000 mAh power bank at 3.7V contains 74 Wh of energy. When converting to 5V USB output, efficiency losses mean the effective charging capacity is lower than the rated mAh suggests.
Electric Vehicle Batteries
EV batteries are measured in kWh (kilowatt-hours). A typical electric car battery rated at 60 kWh equals 60,000 Wh. At a nominal voltage of 400V, this would be equivalent to 150,000 mAh or 150 Ah (amp-hours).
Drone and RC Batteries
RC hobbyists use lithium-polymer batteries with varying voltages (7.4V, 11.1V, 14.8V for 2S, 3S, 4S configurations). A 5000 mAh 3S battery (11.1V) provides 55.5 Wh, determining flight time based on motor power consumption.
Why Voltage Matters
The same mAh capacity at different voltages produces vastly different energy amounts. This is why you cannot directly compare batteries by mAh alone.
Comparison Example
Battery A: 2000 mAh at 3.7V = 7.4 Wh
Battery B: 2000 mAh at 7.4V = 14.8 Wh
Battery B stores twice the energy despite having the same mAh rating. This demonstrates why watt-hours provide a more accurate measure of battery capacity.
Note: When comparing battery capacities across different devices or applications, always convert to watt-hours for accurate comparison. Airlines also use Wh limits (typically 100 Wh) for carry-on batteries, not mAh limits.
Related Conversions
Frequently Asked Questions
What is the difference between mAh and Wh?
mAh (milliamp-hours) measures electric charge or battery capacity – how much current a battery can deliver over time. Wh (watt-hours) measures energy – the actual amount of work the battery can perform. Wh provides a more complete picture of battery performance because it accounts for both capacity and voltage.
Can I convert mAh to Wh without knowing the voltage?
No, voltage is required for this conversion. The formula Wh = (mAh × V) ÷ 1000 requires the voltage value. Without it, you cannot determine the energy capacity. Check the battery label, manufacturer specifications, or device manual to find the voltage.
Why do power banks show different mAh for input and output?
Power banks store energy at one voltage (typically 3.7V) but output at another (usually 5V for USB). The internal battery might be 10000 mAh at 3.7V (37 Wh), but when converting to 5V output with ~85% efficiency, the effective output is about 6300 mAh at 5V. The Wh rating remains more consistent across voltage conversions.
How do I calculate battery runtime?
Runtime (hours) = Battery Capacity (Wh) ÷ Device Power Consumption (W). For example, a 37 Wh battery powering a 10W device will run for approximately 3.7 hours. This calculation is more accurate than using mAh because it accounts for voltage differences.
What is the airline limit for lithium batteries?
Most airlines allow lithium batteries up to 100 Wh in carry-on baggage without approval. Batteries between 100-160 Wh typically require airline approval. This is why Wh is the standard measurement for air travel battery restrictions, not mAh.
Is a higher mAh rating always better?
Not necessarily. A higher mAh at lower voltage might contain less total energy than a lower mAh at higher voltage. Always compare batteries using watt-hours (Wh) for accurate capacity comparison. Additionally, consider factors like charging speed, cycle life, and weight.
How does temperature affect battery capacity?
Battery capacity decreases in cold temperatures and can be damaged by excessive heat. The mAh and Wh ratings are typically measured at room temperature (20-25°C). At 0°C, lithium-ion batteries may deliver only 70-80% of their rated capacity. Always store and use batteries within the manufacturer’s recommended temperature range.
What does the C-rating mean for batteries?
The C-rating indicates discharge rate capability. A 1C rating means the battery can discharge its full capacity in 1 hour. A 2000 mAh battery with a 2C rating can safely discharge at 4000 mA (4A). This is crucial for high-drain applications like drones and RC vehicles where power demand is high.
Battery Chemistry and Voltage
| Battery Chemistry | Nominal Voltage | Applications |
|---|---|---|
| Alkaline | 1.5V | AA, AAA, C, D batteries |
| NiMH (Nickel-Metal Hydride) | 1.2V | Rechargeable AA/AAA |
| NiCd (Nickel-Cadmium) | 1.2V | Older rechargeable batteries |
| Li-ion (Lithium-ion) | 3.6V – 3.7V | Phones, laptops, 18650 cells |
| LiPo (Lithium Polymer) | 3.7V | Drones, RC vehicles, thin devices |
| LiFePO4 (Lithium Iron Phosphate) | 3.2V – 3.3V | Solar systems, electric bikes |
| Lead Acid | 2V per cell | Car batteries (6 cells = 12V) |
| Zinc-Carbon | 1.5V | Low-drain devices |
Practical Applications
Solar Power Systems
When designing off-grid solar systems, battery banks are sized in Wh or kWh. If your daily consumption is 5 kWh (5000 Wh) and you use 12V batteries, you need batteries totaling approximately 417 Ah (417,000 mAh). Converting between these units helps in system planning and component selection.
Emergency Backup Power
For emergency power calculations, knowing the Wh capacity of your batteries helps determine backup duration. A laptop consuming 45W powered by a 74 Wh power bank (20000 mAh at 3.7V) will run for approximately 1.6 hours, accounting for conversion efficiency.
Camping and Outdoor Activities
Portable power stations are rated in Wh, making it easy to calculate how many times you can charge devices. A 500 Wh power station can theoretically charge a 3000 mAh phone (11.1 Wh at 3.7V) about 45 times, though real-world efficiency reduces this to approximately 35-40 full charges.
Efficiency Considerations
Real-world battery performance differs from theoretical calculations due to several efficiency factors:
- Voltage Conversion Loss: Converting between voltages (e.g., 3.7V to 5V) typically loses 10-20% efficiency
- Heat Dissipation: Energy lost as heat during discharge reduces usable capacity
- Age and Cycle Count: Batteries lose capacity over time and charge cycles
- Discharge Rate: Higher discharge rates reduce effective capacity
- Temperature Effects: Cold temperatures significantly reduce available capacity
- Internal Resistance: Causes voltage drop under load, reducing effective energy delivery
Practical Tip: When planning battery capacity needs, add a 20-30% buffer to account for efficiency losses, aging, and temperature variations. This provides a more realistic estimate of actual usable capacity.