How to choose a power bank
If you want better phone battery life a power bank will ensure your handset always has enough charge,
Phones get faster every year, but the more powerful they become the less their batteries can keep everything going. And, of course, all batteries will degrade over time. If you need extra battery power for your smartphone, tablet or other USB-powered device, you need a power bank.
You might assume all power banks are much the same thing, but you would be wrong. You can get compact power banks that will charge your phone
once, slightly larger portable chargers that might offer two or three charges, or high-capacity banks that can charge your phone in excess of 10 times!
Working out how many times a power bank will charge your phone depends on more than the mAh rating on the packaging. No power bank is 100 percent energy-efficient, with every portable charger losing power through voltage conversion and heat generated. The industry standard for energy efficiency is between 60- and 70 percent, and if it doesn’t expressly state otherwise on the packaging this is likely what you’ll get. But some of the best power banks can offer as high as 90 percent energy efficiency, which equates to more full charges for your phone.
Power banks can also vary greatly on their inputs and outputs. We’re seeing an increasing number of power banks with support for the latest Quick Charge 3.0 and USB-C standards, and in some cases these are supported on the input as well as the output, making them as fast to refill as they are to charge your phone. Some power banks may offer these in place of or alongside full-size USB, Micro-USB and even Lightning ports - which you choose entirely depends on which connection your phone uses, and for how long you intend to keep that phone until you upgrade. (Most power banks are guaranteed for 500 recharges.)
Typically you will need to carry a Micro-USB cable to charge your power bank, and potentially another cable for charging your phone if it doesn’t use the Micro-USB connection to charge. Some power banks come with carry cables to ease this requirement; others might feature built-in cables
and Micro-USB-to-Lightning adaptors, so all you need throw in your bag is the power bank itself.
We’re starting to see power banks creep on to the market that feature an AC/DC outlet – a plug socket that allows you to plug in much more than USB devices. Unfortunately, so far we’ve seen only power banks with the US two-pin plug, and needing to carry around a UK three-pin adaptor makes them less easily portable and feel less convenient.
Another type of power bank builds in solar panels. You might think living in the UK our grey climate would rule out the use of such a device, but even in cloudy conditions these devices can draw some solar power. However, the sunnier the conditions the better they work, so if this is the kind of device you’re after we’d recommend a model with a built in battery that means you will have power for your phone even when it’s dark outside.
Design is important when it comes to choosing a power bank, and some batteries are more compact than others at the same capacity. You can also buy those protected from the elements, but be sure
to check whether they are probably waterproof or rainproof before leaving them out in the cold.
The ideal power bank is one that’s small enough to slip into a pocket or bag without it weighing you down, but with enough juice to keep your phone going all day long. Something exactly like the Zendure A2 that sits at the top of our chart: it’s fast, it’s compact, it’s got enough power to charge your phone two- to three times, and it has a sufficiently durable casing that you could even run it over in your car.
Nearly all power banks use a series of (typically four) LEDs to show you how much power remains in the device. This is fine for smaller-capacity devices, but when each LED represents two- to three full charges for your phone it can be difficult to see exactly where you are. We favour power banks with built-in LCD screens, though you will usually pay a little more for the privilege. No power bank we’ve tested has a more informative and useful LCD screen than the Omnicharge.
Advanced features
Next we come on to the more advanced features that are useful to have but not always found in cheaper power banks. Passthrough charging is something we always look for, and is the ability to charge a connected smartphone at the same time as the device itself. Some power banks say they support passthrough charging, but will actually prioritise the connected device until its battery is full, all the while trickle-charging the power bank itself with whatever power is going spare, then turn their attention to the bank itself. Others will charge both devices at full-speed at once.
Auto-on and auto-off is another sought after feature, though it’s worth pointing out that sometimes a power bank can support this but your phone won’t. It means you can plug in a phone to charge and the power bank will instantly begin doing its thing without you pressing any buttons. And when charging is complete it will put itself into standby mode in order to conserve energy.
Some power banks, though it’s an increasingly rare feature, also come with an LED torch that will usually be activated by double-pressing a button somewhere on the casing. We’re not massive fans of the built-in torch, though we do understand it can come in useful in certain situations, such as camping. In most cases, though, the rather weak LED is of little use in all but the darkest conditions.
Charging and recharging
The input rating is key when it comes to recharging the power bank – the higher is this figure the more quickly it will charge. You’ll usually see a figure in
Amps, for instance 1A. You multiply this number by the voltage (5V for USB) to find the rating in Watts. A 1A input can charge at 5W, therefore, but you’d do better to look for a device that can charge at 2A (10W).
Don’t expect to get a USB charger in the box – you can use that which was supplied with your phone or tablet. Do note, however, that a power bank with a 2A (10W) input will not recharge its own battery any faster than one with a 1A (5W) input when used with an underspecified USB charger. The reverse is also true when it comes to charging your devices – a phone that supports only a 1A (5W) input won’t charge faster from a 2A (10W) output.
The output rating refers to how quickly a power bank will charge your devices. In most cases you’ll find 1A (5W), 2A (10W) and often even 2.5A (12.5W) outputs, the former intended for smartphones and the latter two for tablets or for fast-charging phones that support the feature. (This is not the same as the Qualcomm Quick Charge feature supported by several flagship phones.) You can use either output to charge any USB device – it will draw only the power it needs. However, you might find some tablets – usually iPads – will refuse to charge from lower-specified outputs.
Increasingly power banks feature clever technology which is often referred to as PowerIQ or similar. This allows the power bank to recognise the type of device you have connected for charging and deliver the optimum amount of power for that device.
If a power bank has several outputs then the maximum total output capacity is key. For example,
the LimeFuel Blast Pro L240X has four 2.4A (12W) outputs, but delivers only 4.2A (21W) total output. With four USB devices attached you will find that each charges much more slowly.
Can you power bank charge your phone in five minutes?
No. Recently, some power banks have hit the headlines for their apparent ability to charge your phone in five minutes. What these power banks are actually able to do is refill their own batteries sufficiently within five minutes that they can then fully charge your phone. How quickly they can supply that power depends firstly on how much power they are able to output, and secondly how much power your phone can accept.
As an example, the Simpiz iTron, uses DUBI 1.0 technology to refill its own 9000mAh battery in 18 minutes. If you consider that as 3000mAh per six minutes, it would certainly have enough power to fully charge most phones within five minutes.
When it comes to then transferring that power to your phone, the Simpiz iTron’s fastest output is Quick Charge 2.0. This is incredibly fast, but if you have or will have one of the latest devices that support Quick Charge 3.0, such as the Xiaomi Mi 5 or LG G5, it’s not actually the fastest charge they are able to accept.