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Power Bank Capacity Formula:
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The real capacity of a power bank refers to the actual usable capacity available at the output voltage (typically 5V for USB devices), accounting for voltage conversion efficiency and energy losses during the conversion process from the internal battery (typically 3.7V).
The calculator uses the power bank capacity formula:
Where:
Explanation: The equation accounts for the energy loss during DC-DC conversion from the internal battery voltage to the output USB voltage.
Details: Understanding the real capacity helps consumers make informed purchasing decisions and set realistic expectations about how many times a power bank can charge their devices.
Tips: Enter the manufacturer's rated capacity in mAh (at 3.7V) and the conversion efficiency (typically 0.85 for most quality power banks). All values must be valid positive numbers.
Q1: Why is real capacity lower than rated capacity?
A: Due to voltage conversion from 3.7V to 5V and energy losses during the conversion process, the actual usable capacity is always lower than the rated capacity.
Q2: What is typical efficiency for power banks?
A: Most quality power banks have efficiency between 80-90%. Lower quality units may have efficiency as low as 70%.
Q3: How many times can a power bank charge my phone?
A: Divide the real capacity by your phone's battery capacity. For example: 5000mAh real capacity / 2500mAh phone battery ≈ 2 full charges.
Q4: Does temperature affect power bank efficiency?
A: Yes, extreme temperatures can reduce efficiency and overall performance. Optimal operation is typically at room temperature.
Q5: Why do some power banks perform better than others?
A: Quality of components, circuit design, and battery cells all contribute to differences in real-world performance and efficiency.