Power Bank mAh Explained: Why 20,000 Isn’t Really 20,000

A "20,000 mAh" power bank will not charge a 4,500 mAh phone four times. It charges it about two and a half times. Nothing is wrong with the power bank — the number on the box is measured somewhere you never use it.

Why the number shrinks

The lithium cells inside a power bank run at about 3.7 volts. Your phone charges at 5 volts or higher. The power bank has to step the voltage up, and that conversion loses energy as heat — typically 30–40%.

So the real maths for a 20,000 mAh bank:

• Rated: 20,000 mAh at 3.7V
• After conversion to 5V: roughly 12,000–13,000 mAh usable at the port
• Charging a 4,500 mAh phone: about 2.5 full charges, less if the phone is warm or you use it while charging

A 20,000 mAh pack in our power banks range is listed with its usable figure — about 12,800 mAh — on the product page, because that is the number that predicts your day.

Wh is the honest unit

Watt-hours (Wh) already account for voltage, so they do not play the same game:

Wh = (mAh ÷ 1000) × voltage 20,000 mAh × 3.7V = 74 Wh

Two power banks with the same Wh hold the same energy, whatever their mAh label says. When you can find the Wh figure, compare on that.

The airline rule

Every airline flying out of Pakistan uses the same limit: power banks under 100 Wh are allowed in carry-on only, never checked baggage.

This is why every power bank on our power banks page lists its Wh figure — so you are not stopped at security.

What actually matters when buying

1. Real usable output, not the headline mAh.
2. Fast-charge output — a PD or QC wattage per port, so it charges your phone quickly rather than trickling.
3. Recharge input speed — a 20,000 mAh bank at 5W input takes all night; at 22.5W it is done in about four hours.
4. A percentage display beats four vague LED dots.

Browse power banks in Pakistan — bank transfer with fast nationwide delivery, honest capacity figures on every listing.