Demystifying Battery Ratings: mAh vs. mWh
- Time of issue:2023-09-22 13:22
Demystifying Battery Ratings: mAh vs. mWh
In the world of batteries, two important metrics come into play: mAh (Milliampere-hours) and mWh (Milliwatt-hours). These ratings are critical for choosing the right battery for your specific needs, whether you're powering flashlights, RC cars, toys, household devices, VR games or outdoor equipment. In this post, we'll delve into the details of mAh and mWh, providing you with a clear understanding of what they mean and how to make informed battery choices.
Understanding mAh and mWh
mAh (Milliampere-hour) is a unit of measurement for battery capacity. It refers to the amount of charge a battery can hold and deliver at a certain current over time. In simpler terms, mAh quantifies how much electrical energy a battery can release within one hour. At the same rated voltage, a higher mAh value indicates a larger capacity, much like a larger reservoir for storing water.
Here's a simple formula to explain the concept of mAh: Q = I * t, where:
· Q represents the battery's charge capacity, measured in mAh.
· I stands for current, measured in milliamperes (mA).
· t denotes time, measured in hours (h).
For example, if a battery has a rated capacity of 2000mAh, it means it can provide a current of 2000 milliamperes (equivalent to 2 amperes) for one hour.
mWh (Milliwatt-hour) is a measure of the total energy stored in a battery. It reflects the energy generated by a battery when operating at a constant power for one hour at different working voltages. In reality, true capacity is closely related to voltage, and the voltage of most batteries is not a fixed value; it can vary during use.
In simple terms, mWh is like measuring the total energy stored in a reservoir, accounting for both depth (voltage) and volume (capacity). This means that mWh provides a more comprehensive view of a battery's energy potential.
Let's use a simple formula again to explain the concept of mWh: W = U * Q, where:
· W represents the energy capacity of the battery, measured in mWh.
· U stands for voltage, measured in volts (V).
· Q is the battery's charge capacity, measured in mAh.
For example, if a battery has a capacity of 2000mAh and a voltage of 3.7 volts (V), its energy capacity would be 7.4 watt-hours (Wh) or 7400 milliwatt-hours (mWh). This means it can provide 7400 mWh of energy.
mAh to mWh Conversion
The conversion between mAh and mWh is based on the voltage of the battery, which can be converted by the following formula:
This conversion is essential, for instance, in aviation regulations regarding the carriage of lithium batteries. These regulations often specify that lithium batteries must not exceed 100 watt-hours (Wh). However, some rechargeable batteries are typically labeled in mAh, which can be quickly converted into mWh.
Why Do Most Batteries Use mAh for Capacity Rating?
Almost all the 3.6/3.7V Li-ion and 1.2V NiMH batteries use mAh in capacity labeling, instead of only label with mWh. What’s the reason?
Using mAh as a unit of measurement is primarily for convenient calculations, allowing users to estimate usage time more intuitively. For example, when using a 20,000mAh power bank to charge a 5,000mAh smartphone battery, we can quickly calculate that it can charge the phone approximately 4 times because both the power bank and the smartphone battery typically use 3.7V batteries.
mAh are easy to calculate, while mWh may involve the complicated issue of the discharge platform. And we have become accustomed to that way in our daily life.
When to Use mWh Ratings with Examples
Comparing Battery Capacities Under Different Voltages
When comparing the capacity of different battery types, using watt-hours (Wh) is a more appropriate method. For example, when comparing the rated capacities of a 2500mAh AA 1.5V lithium-ion battery and a 1.2V NiMH battery, it's essential to compare their mWh ratings. By calculation, we can determine:
2500mAh x 1.5V = 3750mWh
2500mAh x 1.2V = 3000mWh
Therefore, the 1.5V AA lithium-ion battery has a higher rated capacity than the 1.2V AA NiMH battery.
For high-energy-consuming devices that require a continuous and stable power supply, such as VR and X-box controllers, mWh labeling is more appropriate. These devices often operate at different voltages, necessitating consideration of voltage differences.
Multiple Battery Assemblies
When multiple battery cells are connected in series or parallel, mWh labeling helps accurately represent the total energy capacity. This is common in devices like laptop battery packs or remote-control toy cars.
Different Device Drivers
If the driver is a linear constant current driver, then essentially it is controlling the current directly coming from the battery, hence mAh is best. If you have a buck or boost driver, then the output power is usually fixed, and efficiency is usually somewhat consistent, hence mWh is a better measurement.
Applications of mAh and mWh
At home, we often use devices with low power requirements, such as TV remote controls and wall clocks. These devices operate at low power and current levels, and since battery replacement is infrequent, prioritizing battery life is essential. In such cases, mAh is the preferred unit of measurement.
For example, a household wall clock consumes about 2 milliwatts of power per hour. If you use a standard AA battery labeled as 3000mAh (rated at 1.5V), it can power the clock for 2250 hours. This illustrates that mAh batteries are highly suitable for devices that require long-lasting battery life and have low power consumption requirements.
In another scenario, when using a 20000mAh power bank to charge a 5000mAh smartphone battery (typically using a 3.7V battery), you can quickly calculate that it can charge the phone four times. Therefore, mAh is used to indicate battery capacity, allowing users to intuitively calculate usage time.
Now, let's enter the realm of medium to high-energy-consuming devices, such as VR controllers, wireless microphones, electric toothbrush, trail cameras, electric RC toys. These devices often require a constant and stable power supply and rapidly consume power to provide a responsive experience. In such cases, mWh becomes the ideal unit of measurement.
Some reputable brand provide both mAh and mWh on battery to let users know the information quickly and easily, no need of calculation. For example, XTAR labels their latest new generation rechargeable 1.5V lithium AA battery with both 4150mWh and 2500mAh.
In summary, our daily lives are filled with a variety of devices, each with its specific power requirements. By understanding the difference between mAh and mWh, we can better choose batteries that meet the energy needs of these devices, ensuring that our electronic devices are always ready to operate.
Whether it's the need for extended battery life, higher power output, or compatibility with different voltages, the key to selection lies in the specific application scenarios. These units of measurement provide crucial information about battery performance and suitability, enabling us to make informed choices.
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