Understanding battery capacity is crucial, whether you're dealing with power banks, laptop batteries, drone batteries, or even electric vehicle packs. You'll often encounter two primary units: Watt-hours (Wh) and milliampere-hours (mAh). While both measure energy storage, they tell slightly different stories about a battery's capability. This calculator and guide will help you easily convert between them.
What is Watt-hours (Wh)?
Watt-hours (Wh) is a unit of energy, representing the amount of electrical work done over a period. It's a more comprehensive measure of a battery's total energy capacity because it takes into account both the current (Amperes) and the voltage (Volts). Essentially, Wh = Volts (V) × Ampere-hours (Ah). This unit is particularly useful for comparing batteries of different voltages, as it gives a true picture of the total energy available.
What is milliampere-hours (mAh)?
Milliampere-hours (mAh) is a unit of electric charge, commonly used to describe the capacity of smaller batteries like those found in smartphones, power banks, and drones. It represents how long a battery can deliver a certain amount of current. Specifically, 1 mAh means the battery can deliver 1 milliampere of current for one hour. While widely used, mAh alone doesn't tell the full story without knowing the battery's voltage. For example, a 5000 mAh 3.7V phone battery holds significantly less energy than a 5000 mAh 14.8V drone battery.
Why Convert Wh to mAh?
The need for conversion often arises for several reasons:
- Device Compatibility: Some devices specify power requirements in Wh, while batteries are often rated in mAh.
- Travel Regulations: Airlines often have restrictions on the maximum Wh capacity of batteries allowed in carry-on or checked luggage. Knowing the Wh of your mAh-rated battery is essential for compliance.
- Accurate Comparison: As mentioned, Wh provides a more accurate comparison of total energy across batteries with different voltages.
- Safety: Understanding the total energy can be important for safe handling and storage.
The Conversion Formula
Converting Watt-hours (Wh) to milliampere-hours (mAh) is straightforward if you know the battery's voltage (V). The formula is:
mAh = (Wh × 1000) / V
Let's break down why this formula works:
- We know that Watt-hours (Wh) = Volts (V) × Ampere-hours (Ah).
- Therefore, Ampere-hours (Ah) = Wh / V.
- Since 1 Ah = 1000 mAh, we multiply the result by 1000 to get milliampere-hours.
Example Calculation:
Let's say you have a power bank rated at 37 Wh and you know its internal battery operates at 3.7V. To find its capacity in mAh:
mAh = (37 Wh × 1000) / 3.7 V
mAh = 37000 / 3.7
mAh = 10000 mAh
So, a 37 Wh, 3.7V power bank has a capacity of 10,000 mAh.
Important Considerations
- Nominal Voltage: Always use the battery's nominal voltage for calculations. This is the average operating voltage, not the peak or minimum voltage.
- Efficiency Losses: The conversion formula provides the theoretical capacity. In real-world usage, there are always efficiency losses during charging and discharging, so the usable capacity might be slightly less.
- Device Voltage vs. Battery Voltage: For devices like power banks, remember that the output voltage (e.g., 5V for USB) is often different from the internal battery's nominal voltage (e.g., 3.7V). Always use the internal battery's voltage for the conversion.
Use the calculator above to quickly and accurately convert your battery's Wh rating to mAh, ensuring you have the right information for your needs.