How we test portable power bank chargers

We independently test power banks of all shapes and sizes from a wide range of manufacturers, so you can rest assured the one you’re buying will live up to its claims.

Our reviews answer the most crucial questions about power banks:

• What kind of power bank is it?
• Does it live up to its claimed capacity?
• How long does it take to charge the power bank?
• How long does it take to charge my devices?
• How portable is it?
• What are the sockets like?
• Should I buy it?

Find out which models deliver the best results in our power bank reviews.

What kind of power bank is it?

We sort power banks into three categories – small, medium and large. Each type excels in its own ways. So while the tests we carry out are the same on every power bank, we rate the results slightly differently for each type.

Small power banks have a claimed capacity of up to 7,500mAh (milliampere hour). That should be enough to charge one smartphone. When buying a small power bank, you’re likely to be most interested in portability, and we weight our test scores to reflect this.

Medium power banks have a claimed capacity of between 7,501 and 14,999mAh. That can be enough to fully charge more than one smartphone. When we rate medium power banks, we’re looking for a balance of power, speed and portability.

Large power banks have a claimed capacity of 15,000mAh. That can be enough to charge multiple smartphones or tablets. Power, speed, efficiency and number of sockets to charge more than one device are all key factors in this category.

Does it live up to its claimed capacity?

Our tests reveal time and time again that many power banks just don’t provide the capacity they claim on the box.

We see power banks with the same claimed capacity supply very different amounts of energy when we put them to the test. That’s why we test every power bank on real devices to see how much charge you’ll get in real-world conditions – something you can’t tell just by looking at the numbers.

How long does it take to charge the power bank?

Some power banks take more than twice as long to charge as other models of the same size. One big advantage of power banks is that you can use them on the go, but that goes out of the window when they take the best part of a day to recharge. We fully drain and recharge every power bank to see how fast they are on their feet, then compare them to their peers.

How long does it take to charge my devices?

You might think that similar power banks would charge devices at similar rates – but you’d be wrong. Some take hours longer to fully charge a device than others. That might be fine if you need to recharge a phone overnight. But it can be a real pain if you’re trying to keep a high-drain device, like a Nintendo Switch games console, or a tablet alive while you’re using it.

What are the sockets like?

We’ve seen our share of sockets, so we know how to sort the good from the bad. Are they clearly marked with the right electrical information? Is it clear which ports you plug your devices into (outputs) and which are used to charge the power bank (inputs)? And are the ports far enough apart to fit in more than one chunky cable when charging more than one device at once?

Should I buy it?

All of the assessments above go into making up the overall score for each power bank we review. Because we know what’s most important to you, some elements carry more weight than others:

• 70% Performance
• 25% Ease of use
• 5% Features

What are Which? Best Buys, Don't Buys and Great Value models?

Best Buys

The power banks that impress the most in our tests are made Best Buys. A power bank must achieve a score of 75% or more to become a Best Buy, but you should still read our reviews to check for any factors that might impact your buying decision. 

Don't Buys

Power banks that receive a score or 45% or below are Don’t Buys and should be avoided - these are likely to deliver far lower than their claimed capacity and be woefully inefficient. They may also be slow to charge devices.

Great Value

A power bank with a Great Value logo has to score at least 65%. They're also at least 20% cheaper than the average cost of other power bank types (small, medium or large capacity) in our tests. 

The Great Value models highlighted by our experts are the ones to go for if you're looking for a bargain – and we've applied the Great Value rating based on the average price of each type, as we know small power banks are cheaper than large power banks. Some Great Value models also score well enough to be a Best Buy.