Why a 10,000mAh Power Bank Isn’t Fully 10,000mAh
If you’ve ever felt a bit shortchanged by a power bank, you’re not alone. Many users find that although a 10,000mAh power bank seems sufficient to charge a flagship phone with a 5,000mAh battery twice, the reality is often more complicated. Usually, about one and a half charges is a more realistic estimate.
Understanding Battery Capacity
The good news is that your power bank isn’t lying. However, the bad news is that battery capacity is a bit more complex than what appears on the packaging. The milliampere-hour (mAh) figure you see doesn’t fully reflect the amount of power your phone will actually receive. This is often where confusion begins.
When buying a new power bank, we tend to focus on the prominent mAh number — a measure we might understand from everyday experience. If our 5,000mAh phone battery lasts all day, then a comparable power bank should be enough for a day trip. But it’s important to remember that mAh is a relative, not an absolute, measure.
Voltage Strength and Its Limitations
The mAh value listed refers to the internal lithium battery capacity based on its "nominal" operating voltage. For Li-Ion batteries, this usually ranges between 3.7 to 3.85V. However, some manufacturers also report their mAh values equivalent to outputs of 5V, 20V, or others, depending on the intended use case.
The first complication arises when the reference voltage of the power bank differs from the device you are trying to charge. For example, your phone may have a nominal operating voltage around 3.6V to 3.9V, while your laptop might range between 11V to 16V. In other words, different devices have specific internal voltage requirements.
Calculating the Actual Capacity
To calculate the actual capacity of our power bank, we can multiply the mAh rating by the nominal cell voltage to get the total average power output per hour, measured in watt-hours (Wh). For example, a 5,000mAh power bank at 3.7V can provide 18.5 Wh, while a 20,000mAh one at 3.6V offers 72 Wh.
However, this efficiency can vary depending on many factors, including the quality of the converter chip and the cables used. Voltage conversion is not always efficient. For instance, DC to DC converters have efficiencies between 85% to 98%, meaning some energy is lost during the process.
Energy Loss During Charging
Additionally, batteries experience internal resistance during charging, causing energy to be lost as heat. Even under the best conditions, charging efficiency often doesn’t reach 100%. On top of that, there are voltage losses along the USB-C cable from the power bank to your phone. Although usually small, these losses can add up when using low-quality cables or when high power is drawn.
For wireless charging, energy loss is even greater. Although technologies like Qi2 and MagSafe offer convenience, they can cause conversion losses of 20% or more.
Overall, all these factors explain why charging a battery from an external source can be disappointing. Energy lost as heat and inefficiencies during conversion contribute to the harsh reality that power banks don’t deliver the "real" capacity you might expect.
So, if you want the assurance that your power bank can fully charge your device twice during a weekend trip, it’s highly recommended to choose a power bank with a larger capacity. A power bank with 70Wh or more could be the solution to ease your power concerns.
Source: https://www.androidauthority.com/why-your-power-bank-feels-small-3675437/
