Every power bank is sold on one number. 10,000. 20,000. 27,000. Bigger number, better product — that's the pitch.

Except a 20,000mAh power bank will not put 20,000mAh into your phone. It isn't false advertising, but it catches people out constantly.

Why 20,000mAh Isn't 20,000mAh

The rating describes the cells inside, which run at about 3.7 volts. Your phone charges over USB at 5 volts. Converting between the two loses energy as heat, and there are further losses in the cable and your phone's own charging circuitry.

Real-world, you get about 60–70% of the advertised figure.

So a 20,000mAh bank delivers roughly 12,000–14,000mAh — about two and a half to three full charges of a typical modern phone. Not the five that some listings imply.

This applies to every brand equally. It's physics, not marketing.

The Airline Rule Most People Miss

Airlines don't measure power banks in mAh. They measure watt-hours:

mAh × volts ÷ 1,000 = Wh
20,000mAh × 3.7V ÷ 1,000 = 74Wh

The usual limit is 100Wh, so 20,000mAh sits comfortably under it. Go much past 27,000mAh and you start needing airline approval.

But here's the rule that actually catches people: power banks must travel in your carry-on, never in checked luggage. That applies at any size. Rules vary by airline and change, so check before you fly.

What Size Should You Buy?

• 5,000mAh — a top-up for a long day. Pocketable, about one charge.

• 10,000mAh — the sweet spot for most people. One and a half to two charges.

• 20,000mAh — weekends away, camping, festivals, or more than one device. Two and a half to three charges, but noticeably heavier.

• 27,000mAh+ — laptops and long trips. Check the Wh before flying.

Bigger isn't automatically better. A heavy power bank you leave at home is worth less than a small one in your bag.

Two Specs That Matter More Than Capacity

Output wattage decides how fast it charges. A big bank with low output refills your phone slowly. If a listing doesn't state wattage clearly, that usually tells you something.

Ports decide whether it's convenient. USB-C in and out means one cable for everything. Also check whether fast charging applies to all ports, or drops when you charge two devices at once. It usually drops.

A 20,000mAh Option

If that's the size that suits you, the INIU 20,000mAh power bank is one to compare against others. It's marketed on being compact for its capacity, which is the main trade-off at this size.

Before buying any power bank, check the output wattage , the port setup, the weight if you'll carry it daily, and read the recent reviews rather than the overall star rating — batteries degrade, so recent feedback tells you more.

Check the current listing on Amazon →

Common Mistakes

• Buying on capacity alone. A slow 20,000mAh bank is more annoying than a fast 10,000mAh one.

• Ignoring recharge time. Big banks take hours to refill.

• Assuming the bundled cable is good. Fast charging needs a cable rated for it.

• Leaving it flat for months. Lithium cells don't like sitting empty. Top it up occasionally.

FAQ

Why doesn't it charge my phone as many times as advertised?

Voltage conversion losses. You get 60–70% of the rated capacity delivered. Every brand is the same.

Can I take a 20,000mAh power bank on a plane?

Generally yes — about 74Wh, under the usual 100Wh limit. It must go in carry-on, never checked luggage. Confirm with your airline.

General information only. Specifications and availability change — check the current listing before buying. Airline battery rules vary by carrier; confirm with your airline and CASA before travelling.

Disclosure: This post contains affiliate links. As an Amazon Associate I earn from qualifying purchases, at no extra cost to you. Prices change often — always check the current listing. #ad