The CHJGD Kaset comes in various designs, of which the company was kind enough to send us two. Other than the styling, each of these power banks are the same and all cost £19.99 direct from CHJGD’s website. We received the Love Songs and Marilyn Monroe versions, and CHJGD also sells 90s Hits, Mixtape and Rock Mix options. Unfortunately both the cases were cracked upon delivery, but the power banks themselves were fine and we have plenty of old cassette boxes up in the loft with which we can replace them. Upon opening the box and removing the insert you’ll find a short flat Micro-USB cable that sits atop the cassette, and you just slide it out the box as you would any cassette. See all power bank reviews The design is really well done, and so much so we nearly missed the power button that is disguised as one of four plastic ‘screws’ in the bottom right corner. Tapping this lights up the four LEDs that show how much power remains, but you wouldn’t notice these when they aren’t lit. It’s not quite the perfect representation, though. There’s no messy tape to get tangled (fortunately), and whereas you might expect to find the various connections on the bottom edge where usually there are holes these are actually on the right side. And we were surprised to find several of them. Also see: How to charge your phone’s battery faster  You won’t find many 6,000mAh power banks with more than one USB output and one Micro-USB input, so we were really pleased to see two full-size USB outputs, Micro-USB AND Lightning. The second input is a great idea, allowing iPhone users to charge up the power bank without having to first hunt down a Micro-USB cable that they would otherwise have no use for. These ports aren’t as fast as we’re used to seeing on CHJGD power banks, but that’s not an enormous problem given the reasonably low capacity – it isn’t going to take hours to refill, and it will sit in your pocket or bag with your phone as you charge it. The Lightning input is rated at 5W, which is ideal for an iPhone charger, and the Micro-USB input at 7.5W. Both USB outputs are rated at 7.5W, which is faster than an iPhone charger but by no means the fastest charger you’ll find for an Android phone and some way off the performance of Quick Charge. Also see: How to improve smartphone battery life The speed at which the Kaset can refill its own battery is less important when you consider that it supports passthrough charging, meaning you can leave both it and your phone plugged in to a single mains outlet overnight. This surprised us, as it’s not always a given. Despite what the user guide says the CHJGD Kaset also supports auto-on, and you simply plug in a mobile device to begin charging. It will turn itself off 60 seconds after you unplug your device if you forget to do so earlier, too. With 6,000mAh of power inside this bank, and an industry standard efficiency of around 65 percent, you should expect around 3,900mAh of usable power. That will offer most iPhones two full charges and most Android phones one full charge. Read next: Best desktop chargers Marie is Editor in Chief of Tech Advisor and Macworld. A Journalism graduate from the London College of Printing, she’s worked in tech media for more than 17 years, managing our English language, French and Spanish consumer editorial teams and leading on content strategy through Foundry’s transition from print, to digital, to online - and beyond.