How to Choose a Power Bank: mAh, W and Ports

September 4, 2026

In short

When choosing a power bank, three numbers matter: capacity (mAh), power (W) and ports. In practice you get about 60–70% of the stated capacity – a 10 000 mAh power bank will charge a phone roughly 1.5 times. For everyday carry, 10 000 mAh and 20–22.5 W is enough; for travel, choose 20 000 mAh; for a laptop, at least 65 W with USB-C PD. Up to 100 Wh is allowed in aircraft hand luggage, i.e. roughly 27 000 mAh.

A power bank is one of those accessories we buy in a hurry before a trip and then regret for the rest of the week. In this guide we explain what the numbers printed on the box really mean and how to choose a power bank that suits your own everyday life.

What does mAh really mean?

Every power bank lists its capacity in mAh – but that is not the amount of energy that will reach your phone. The reason is technical: the internal lithium cells run at about 3.7 V, while the phone charges at 5 V and higher. The voltage has to be stepped up, and some of the energy is lost as heat during the conversion.

Practical formula:

How many times it will charge my phone ≈ (power bank mAh × 0.65) ÷ phone battery mAh

Example: a 10 000 mAh power bank and a phone with a 4 000 mAh battery → (10 000 × 0.65) ÷ 4 000 ≈ 1.6 times. Not three, as you might like to believe.

Stated capacity	Actual output	Phone charges	Weight
5 000 mAh	~3 250 mAh	0.7–0.8	~100 g
10 000 mAh	~6 500 mAh	1.3–1.6	~200 g
20 000 mAh	~13 000 mAh	2.6–3.2	~350–400 g
30 000 mAh	~19 500 mAh	4–5	~550–650 g

How many mAh do I actually need?

5 000 mAh – an “emergency” option for your pocket or handbag. It barely weighs the phone down, especially if it is magnetic. Example: 3mk Hardy MagSynergy 5 000 mAh.
10 000 mAh – the best compromise for everyday use. One full charge with some to spare, and it fits in a pocket. The most popular category.
20 000 mAh – for a weekend, a festival or a trip for two. Charges a phone ~3 times, or two phones at once.
30 000 mAh and more – for camping, long trips and laptops. Heavy, but the only option when there is no socket for several days.

How many watts (W) do you need?

Capacity tells you how much, while power tells you how fast. This is where many people get confused, because a cheap 20 000 mAh power bank can charge more slowly than an expensive 10 000 mAh one.

Power	What it will charge	Phone 0→50%
5–10 W	A phone slowly, earbuds, a watch	~1.5 h
20–22.5 W	A phone quickly (PD / QC)	~30 min
45–65 W	Tablet, ultrabook, Steam Deck	~25 min
100 W and more	MacBook Pro, powerful laptops	~20 min

PD (Power Delivery) is the universal USB-C fast-charging standard – it works with iPhone, Samsung, Android, tablets and laptops. QC (Quick Charge) is Qualcomm's standard, more common on older Android phones. If you are choosing one, choose PD.

An important detail: power is often shared between ports. A 65 W power bank charging two devices will give each of them roughly 30 W. If you plan to charge several devices at once, buy one with power to spare.

Ports and built-in cables

Today the standard is USB-C in both directions – the same cable charges both the power bank and the phone. A USB-A port is still useful for older accessories.

Models with built-in cables deserve a special mention – you simply cannot leave the cable at home:

Dudao K13 10 000 mAh – compact, with a built-in cable.
Dudao K32 22.5 W – comes with both USB-C and Lightning cables, ideal for a mixed Apple/Android household.
Dudao K14+ 20 000 mAh – the same idea in a larger capacity.
Cuktech LPB252N 120 W 25 000 mAh – a built-in cable that can handle laptop-level power.

Is a magnetic (MagSafe / Qi2) power bank worth it?

A magnetic power bank snaps onto the back of the phone and charges it wirelessly – you can keep using the phone and don't need a cable at all. There are two trade-offs: wireless charging is slower and warmer than wired charging, so in practice you get less out of it than from a regular power bank of the same size.

Worth it if you use your phone on the move. Not worth it if the power bank stays in your backpack – then a cable is more efficient.

Wozinsky 10 000 mAh magnetic – the most affordable way in.
Tech-Protect PB31 MagSafe 10 000 mAh.
Cuktech WPB100 with stand – Qi2 wireless charging up to 15 W, up to 30 W by cable, and a fold-out stand for video calls.
Joyroom JR-PBM08 Pro – wireless charging and two USB-C ports.

iPhones from the 12 series onwards (except the iPhone 16e) and the Google Pixel 10 and Pixel 11 series have magnets built in. If the phone is in an ordinary case or has no magnets (for example the iPhone 16e or the Samsung Galaxy S25 and S26), the power bank will hold poorly or not at all – you will need a case with a magnet ring. More on this in our MagSafe and Qi2 guide.

Can you take a power bank on a plane?

Yes, but with conditions that are the same at almost every airline:

Hand luggage only. Lithium batteries are not allowed in a suitcase that travels in the hold.
Up to 100 Wh – allowed without special permission. That is roughly 27 000 mAh.
100–160 Wh – requires the airline's approval.
Over 160 Wh – prohibited.

The conversion is simple: Wh = mAh ÷ 1000 × 3.7. So 20 000 mAh ≈ 74 Wh (allowed), while 30 000 mAh ≈ 111 Wh (you will already need to ask). Quality power banks have the Wh value printed on the casing – it is worth checking before your flight.

Also note: more and more airlines restrict using a power bank during the flight, or require you to keep it in view rather than in the overhead locker. Check the specific airline's rules before you travel.

Best picks by need

Need	What to look for	Example
Cheapest option	10 000 mAh, 10 W	Wozinsky W11 with built-in cables
Everyday carry	10 000 mAh, 22.5 W, USB-C PD	Dudao K32
No cable, on the phone	Magnetic, ideally with Qi2	Cuktech WPB100 with stand
Travel / festival	20 000 mAh, 2 ports	Dudao K14+
Laptop	65–120 W USB-C PD	Cuktech 100 W 20 000 mAh
Several days without a socket	30 000 mAh, 65 W	Wozinsky K65+ 30 000 mAh

Frequently asked questions

Why won't a 10 000 mAh power bank charge my phone three times?

Because of voltage conversion losses. The internal cells run at 3.7 V, while the phone charges at 5 V and higher, so in practice about 60–70% of the stated capacity is delivered. This is normal and applies to all power banks, not just cheap ones.

Can I leave a power bank charging overnight?

Quality power banks have overcharge protection, so they stop drawing power once they reach 100%. Even so, it is better not to charge one on a bed, a sofa or under a blanket – the key thing is that the heat has somewhere to go.

How do I look after a power bank so it lasts longer?

Don't leave it fully discharged for long periods, avoid cold and heat (a car interior in summer is the worst place), and if you won't be using it for a long time, store it at about 50–60% charge and top it up once every few months.

Is a power bank suitable for earbuds and a watch as well?

Yes, via USB-C or USB-A. Some power banks also have a separate wireless charging pad for a watch – for example the Joyroom JR-W19 with 5 W watch charging.

How long does the power bank itself take to charge?

It depends on the input power. A 10 000 mAh power bank with a 20 W input charges in ~2 h, while with 5 W it takes 6–8 h. Input power is often listed separately from output power, so it is worth checking the specifications.

Is a heavier power bank always better?

No. Weight is directly proportional to capacity, and the biggest mistake is buying a 30 000 mAh one “just in case” and giving up carrying it after a week. The best power bank is the one you actually take with you.

Related sections: Power banks · Chargers · Cables · Phone cases

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