Picking a power bank size

A 10,000 mAh power bank is the right size for most people: it gives about 1.5 charges of an iPhone 18 Pro and fits a pocket. A 20,000 mAh power bank suits a weekend away or a laptop top-up, at about 3.0 iPhone 18 Pro charges or 0.87 of a MacBook Air 13 charge. The UK flight limit of 100 Wh works out at about 27,000 mAh, so anything above that needs airline approval.

Every figure here uses the method from Compare Electronic's Best power bank UK 2026 guide: rated watt-hours multiplied by 0.65 for the energy that reaches the device. The picks are the same, at Amazon UK prices on 3 October 2026: the UGREEN Nexode Power Bank 20000mAh 130W at £49.96, the Anker Nano Power Bank 10K 30W at £39.99, the Anker MagGo Power Bank 10K at £47.49 and the INIU 10000mAh at £19.99.

Why does a power bank deliver less than its mAh rating?

A power bank delivers about 65% of its rated capacity because the mAh figure describes the internal cells at 3.6 to 3.85 V, not the energy that reaches a phone. The bank boosts the voltage to 5, 9, 15 or 20 V for USB-C, the phone steps it down again to fill its own battery, and both conversions lose energy as heat.

Watt-hours are the honest unit, because they include the cell voltage: mAh multiplied by volts, divided by 1,000. Two 10,000 mAh banks can differ by 7%: the Anker Nano Power Bank 10K is rated at 36 Wh (3.6 V cells) and the Anker MagGo Power Bank 10K at 38.5 Wh (3.85 V), according to Anker. Wireless charging over Qi2 loses more again than a cable.

How many charges does each power bank size give?

A 5,000 mAh bank gives 0.7 of an iPhone 18 Pro charge, a 10,000 mAh bank 1.5, a 20,000 mAh bank 3.0 and a 26,000 mAh bank 3.9, on Compare Electronic's estimate. For laptops, only a 26,000 mAh bank clears one full MacBook Air 13 charge.

Read the table the other way round to size a bank for a device. One full charge costs about this much rated capacity:

• iPhone 18 Pro: about 6,700 mAh of power bank per full charge.
• Galaxy S26 Ultra: about 8,300 mAh of power bank per full charge.
• MacBook Air 13 (M5): about 23,000 mAh of power bank per full charge.
• ThinkPad X1 Carbon Gen 13: about 24,400 mAh of power bank per full charge.

The laptop columns only apply to a bank that supplies the laptop's minimum wattage. A bank that delivers less than the 30 W Apple sets as the MacBook Air minimum, such as the 20 W INIU 10000mAh, cannot charge it in practice. Cold weather, a warm phone and wireless charging all push real results below every figure here.

How many mAh power bank is good for an iPhone?

A 10,000 mAh power bank is the right size for an iPhone: about 1.5 charges of an iPhone 18 Pro in 195 to 250 g. A 5,000 mAh magnetic pack gives 0.7 of a charge, which covers an evening but not a full day, and a 20,000 mAh bank gives 3.0 charges at 420 g.

The choice inside the 10,000 mAh class is cable or magnet. The Anker MagGo Power Bank 10K is Qi2 certified, snaps onto any iPhone from the iPhone 12 onwards and charges at 15 W wirelessly or 27 W over USB-C, rated by Anker, for £47.49. Wireless charging wastes more energy as heat, so its 1.6 wired iPhone 18 Pro charges drop when used magnetically. The INIU 10000mAh gives about 1.5 charges over a cable for £19.99, about 83p per usable Wh.

Which 20,000 mAh power bank is best?

The UGREEN Nexode Power Bank 20000mAh 130W is the best 20,000 mAh power bank, at £49.96 on Amazon UK at the time of writing (October 2026). UGREEN rates it at 72 Wh with 100 W from one USB-C port and 130 W across its ports, which makes it the smallest bank in this guide that fast-charges both a phone and a laptop.

On Compare Electronic's estimate the UGREEN Nexode's 72 Wh becomes about 46.8 Wh at the device: 3.0 iPhone 18 Pro charges, 2.4 Galaxy S26 Ultra charges or 0.87 of a MacBook Air 13 charge. That is £1.07 per usable Wh. The cost is bulk: about 420 g, more than twice the Anker Nano Power Bank 10K's 215 g.

How many mAh power bank can charge a laptop?

A power bank of any size can charge a laptop if it supplies the laptop's minimum USB-C wattage, but a full MacBook Air 13 charge needs about 23,000 mAh of rated capacity. Apple says the 13-inch MacBook Air with M5 needs at least 30 W and fast-charges from 70 W. Lenovo ships the ThinkPad X1 Carbon Gen 13 with a 65 W USB-C adapter.

Wattage rules out two of the four picks here. The INIU 10000mAh delivers 20 W over USB-C and the Anker MagGo Power Bank 10K 27 W, both below Apple's 30 W minimum; the Anker Nano Power Bank 10K meets it at exactly 30 W but gives only 0.43 of a MacBook Air charge. The UGREEN Nexode Power Bank 20000mAh 130W delivers 100 W from one port, so it fast-charges both laptops, and adds 0.87 of a MacBook Air 13 charge or 0.82 of a ThinkPad X1 Carbon Gen 13 charge. A full charge with spare needs a bank close to 100 Wh. Laptops that need less topping up are ranked in Best laptop UK 2026.

How many mAh power bank is allowed on a flight?

UK flights allow power banks up to 100 Wh without airline approval, which is about 27,000 mAh for typical 3.6 V to 3.7 V cells. Under the UK Civil Aviation Authority provisions effective from 27 March 2026, passengers may carry two power banks each, in hand luggage only, and must not recharge them on board.

• 10,000 mAh (36 to 38.5 Wh): allowed, no approval.
• 20,000 mAh (72 Wh): allowed, no approval. The UGREEN Nexode is rated at 72 Wh.
• 26,000 to 27,000 mAh (about 94 to 99.9 Wh): allowed, no approval, close to the line.
• 30,000 mAh (108 to 111 Wh): needs the airline's approval before travel.
• Above 160 Wh: not permitted as passenger baggage.

Airlines can be stricter: Wizz Air and Emirates limit passengers to one power bank, and most UK airlines ban using one in flight. The airline-by-airline rules are in Can you take a power bank on a plane? UK rules 2026.

What size power bank should you buy?

Buy 10,000 mAh for a phone, 20,000 mAh for a weekend or a laptop, and stay under about 27,000 mAh for flights. Compare Electronic's decision table matches each use to a size and a pick, at Amazon UK prices on 3 October 2026.

Phones with bigger batteries shift the maths. The Galaxy S26 Ultra carries 5,000 mAh, about 23% more than the iPhone 18 Pro, so a 10,000 mAh bank gives it 1.2 charges rather than 1.5. Buyers whose phone already lasts a full day may need nothing larger than 10,000 mAh; the longest-lasting phones are ranked in Longest battery life smartphones 2026.

Which 10,000 mAh power bank should you buy?

The INIU 10000mAh is the best value 10,000 mAh power bank at £19.99, and the Anker Nano Power Bank 10K 30W is the best to carry, at £39.99 on Amazon UK at the time of writing (October 2026). The INIU stores 37 Wh, weighs 195 g and delivers 20 W over USB-C Power Delivery and 22.5 W over USB-A, rated by INIU.

The Anker Nano Power Bank 10K 30W stores 36 Wh and builds a USB-C cable into the body that doubles as a strap, so there is no lead to forget. Anker rates it at 30 W in and out and 215 g. It costs £1.71 per usable Wh against the INIU's 83p, and the extra money buys the cable, 10 W more output and a faster recharge. The Anker MagGo Power Bank 10K at £47.49 is the third option, for iPhone owners who want no cable at all.

Verdict

A 10,000 mAh power bank is good for a phone and a 20,000 mAh bank is good for a weekend or a laptop. The INIU 10000mAh at £19.99 and the Anker Nano Power Bank 10K 30W at £39.99 each give about 1.5 iPhone 18 Pro charges; the Anker MagGo Power Bank 10K at £47.49 does the same without a cable. The UGREEN Nexode Power Bank 20000mAh 130W at £49.96 gives about 3.0 iPhone charges or 0.87 of a MacBook Air 13 charge, and at 72 Wh it flies without airline approval. Nothing above about 27,000 mAh belongs in a UK traveller's hand luggage without asking first. The full shortlist and price per usable Wh are in Best power bank UK 2026.