We come on to the more advanced features that are useful to have but not always found in cheaper power banks....
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 or tablet 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.