Best portable power bank chargers: Which? Best Buys and expert buying advice

Power banks act as portable chargers for your devices, allowing you to stay topped up on the go – but they aren’t all made equal.
William O'Connor
Two women use power bank charger

While the numbers may look the same on paper, there are big differences between the best and worst power banks we’ve tested. 

And it's not just performance that matters – which size power bank you choose, and what additional features and connections it offers, can determine whether it's suitable for you.

Read on for our top tips on buying a great portable power bank.

To see which portable power bank chargers topped our tests, head to our portable power bank charger reviews.

Best portable power bank chargers

Below are the top scoring large, medium and small power banks. To see the cheapest power banks that we recommend, take a look at our guide to cheap power banks for 2024.

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Table last updated March 2024

Should I choose a high, medium or low capacity power bank?

The answer to this will depend on your needs. Small power banks can be great for an occasional top up of power on the go – they’re light enough that you’ll hardly feel the weight of them in your bag. Large models give you more juice, but are less portable. 

  • Small power banks (up to 7,500mAh) - usually enough to charge a smartphone once
  • Medium power banks (7,500-14,999mAh) - usually enough to charge a smartphone 2 times
  • Large power banks (more than 15,000mAh) - usually enough to charge a smartphone 4 or more times

We find that medium power banks, around 10,000mAh, tend to deliver the best balance of portability and capacity. In our tests, they’re also more likely to live up to their claimed capacity. They tend to have multiple ports for charging more than one device at once, and enough energy to charge two smartphones. A Best Buy medium power bank is a great all-rounder.

Large power banks are perfect for heavy-duty use. That could mean charging a single smartphone over a week in the wilderness, or keeping your whole family’s devices alive on long journeys or days out. But aside from their bulk, they also take a long time to recharge. We’ve seen models that take as long as 14 hours to fully recharge, while others take less than 10, so it pays to do your research before you buy.

Still deciding which kind is right for you? See our full list of expert power bank reviews.

Which power banks will work with my phone?

Most power banks will work with any phone. The biggest factor in whether you’ll be able to use one with your phone is the cable. If the cable you’re using doesn’t fit the power bank, you can almost certainly buy one that will.

What connections should I look for on a power bank?

Input ports

Input ports are used to charge a power bank. These tend to be either micro USB or USB-C, and you'll usually find the charge cable comes supplied, and can be plugged into any USB-A mains adaptor, or for instance, the USB port on your laptop.

Micro USB (input)

This is a popular cable type for charging power banks, older smartphones and other small devices - so there's a good chance you already have some around your home. Unlike USB-C and Lightning, micro USB cables need to plugged in the right way around - which can make them fiddly at times.

Lightning (input)

This has been Apple's go-to proprietary cable since the iPhone 5. Like USB-C it's reversible, so can be plugged in either way up. Models with Lightning inputs might suit you if you're an Apple user and you want to minimize the number of cables you need. Rumours have been circulating for years that Apple may move away from the Lightning cable in future releases.

Output ports

Output ports are used to transfer power from the power bank to your devices. Usually, this will be one or more classic USB-A ports. These allow you to plug in your own charger cable, meaning you can likely use whatever cable you’re already using to charge your device.

Some power banks come with a built-in output cable, which can’t be removed. This is usually an extra output, so it shouldn’t affect you if you plan to use other types of cable too.

USB-A (output)

This port is designed for the classic chunky USB cable. While USB-A ports are slowly disappearing from laptops, they're still among the most popular and versatile cable types.

Almost all power banks feature at least one USB-A output.

USB-C (input/output)

This is the recent standard in USB, and is used in most new Android phones. Unlike the other sockets we've mentioned, USB-C can be used either as an input or and output port. This type of cable supports 'power delivery' (more on that later). USB-C connections are also reversible, so there's no chance of plugging them in upside down.

We also measure and rate the distance between sockets. Socket spacing isn’t usually an issue, but it might prevent you getting the most out of your power bank if you’re using chunky or awkwardly shaped cables.

Power bank man outdoors

Do power banks deliver the power they promise?

Yes and no. Most technically deliver on the mAh (milliamp hours) they promise, but that’s not the full story when charging devices. That’s because the batteries inside a power bank are 3.7v, while USB (which is used to charge your devices) runs at 5v. Since mAh is related to voltage, mAh changes when the voltage does. 

To calculate the mAh you’ll actually get when charging devices, multiply the claimed capacity by 3.7 then divide that figure by five (or whatever voltage you’ll be charging at).

To further complicate matters, some energy is also lost through heat. The energy lost can be as low as 15% with some models, but can be much higher in others.

To put this into context, the battery in an iPhone 12 is 2,815mAh. At first glance, a 10,000mAh power bank should be able to charge an iPhone 12 at least three times. At 5v though, a power bank advertised as 10,000mAh is really delivering 7,400mAh (10,000 x 3.7 / 5). Subtract 15% due to energy loss and you’re looking at something closer to 6,290mAh – enough to charge the device just over two times. This is a much more realistic figure based on our extensive testing.

How quickly will a power bank charge my device?

That depends on the model – and we report on this in our tests.

Certain technologies can help to improve standards here, which will appeal if fast charging is important. Power delivery, or 'PD', is one of several fast charge technologies, designed to speed up the time it takes for your power bank to charge your devices. It does this by increasing the wattage used to charge to the maximum amount your device can safely handle. This only works with compatible USB-C cables, which have specialised chips that prevent overheating.

This feature requires a compatible USB-C cable to work. Some models with power delivery have been among the fastest we've tested, but some models without are just as fast.

What else should I look out for when buying a power bank?

Some power banks allow for pass-through charging, while many do not. Pass-through charging means you can charge the power bank while using it to charge your devices. That can be useful when travelling, as it means you won’t need to pack as many adaptors.

It’s not the most efficient way to charge devices though, so it’s usually worth using a regular adaptor if you have time.

Most power bank displays are just a series of four LED lights that light up to show you roughly how much charge there is. Some have numerical displays that show you this as a percentage. That’s handy if you like to micromanage your devices, but it can also take up more space, meaning a slightly bulkier power bank. 

Can I take my power bank on a plane?

Lithium ion batteries, including most power banks, can be carried on planes as hand luggage, but should not be kept in the hold. You may need special permission to carry any battery rated at more than 100Wh (watt hours). That’s around 27,000mAh, which is quite large. 

You may be asked for detailed information on the power bank. This is usually printed on the device, but can rub off with frequent use. If it’s close to the limit and you can’t prove it’s under 100Wh, be prepared for it to be confiscated.

If you’re unsure, check the restricted items section on your airline’s website.

How we test power banks

We subject portable power bank chargers to a rigorous battery of tests to separate bold manufacturer claims from reality. So we know from experience that there's more to buying a power bank than reading the numbers and features on the box.

For instance, some of the best power banks can fully charge your smartphone in one hour 45 minutes, while the slowest take as long as three and a half hours. That's fine if you're charging overnight, but if you need a quick burst of power on a high drain device like a tablet, you'll struggle to charge it faster than it consumes energy.

Other power banks overpromise when it comes to the amount of charge they actually deliver. The worst we've tested only put out 77% of its stated mAh capacity. The best can sometimes actually deliver more than they claim.

Check our power bank reviews to see which models came out on top.