To convert a power bank from mAh to mWh, you need to know the voltage (V) of the battery.
Key formula
mWh = mAh × V
Why this works
mAh = charge capacity
mWh = energy capacity
Energy depends on both charge and voltage
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Typical power bank case (important)
Most power banks use lithium-ion cells at ~3.7 V nominal internally.
So:
mWh ≈ mAh × 3.7
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Example
A 10,000 mAh power bank:
10,000 × 3.7 = 37,000 mWh
So it’s about 37 Wh (watt-hours).
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If you want USB output equivalent:
USB output is usually 5 V, so manufacturers sometimes quote “usable capacity” differently due to voltage conversion losses (typically ~80–90% efficiency).