In design the ultra-slim Vinsic Power Bank is very well designed, clad in dark grey aluminium alloy with hard plastic screwed into either end. It feels reassuringly tough, and although it’s heavy at 537g you wouldn’t expect to cart around on your person such a high-capacity power bank for day-to-day use. Its dimensions aren’t suited to a pocket, either.  Also see: Best MiFi 2016. We particularly like the digital power display at one end of the device, which is activated merely by touching the area to the left of the Micro-USB input. This gives you an exact percentage readout of how much power remains in the bank, so you always know how many more charges you can expect before needing to refill the device. It’s so much easier to work with than the four-LED status lights favoured by most rival power banks. Also see:  How to improve smartphone battery life.    With 20,000mAh of power to hand, and an efficiency rate of around 70 percent (some power is lost though voltage conversion and heat generated), the Vinsic will refill an iPhone 5s 9.1 times, an iPhone 6 7.4 times, iPhone 6 Plus 4.6 times and a Samsung Galaxy S5 4.8 times. Exactly how many times it will charge your phone or tablet will depend on the capacity of its own battery, but expect at least 14,000mAh to be available.  Of course, with two USB outputs you can simultaneously charge both phone and tablet from the Vinsic Power Bank. With one rated at 5W and the other 10.5W, you can plug a phone or tablet into either output but the 5W port is better suited to smartphones than it is tablets. Also see:  How to charge your phone or tablet faster.   Once the power bank’s charge has depleted, you’ll find it much faster to refill than the EC Tech, too, with a 10- rather than 6W input. It charges over Micro-USB, so just plug the supplied Micro-USB cable into the USB charger that came with your phone or tablet and you’re good to go.   Bearing in mind that the Vinsic will take at least a full overnight charge, it’s only a shame that it doesn’t support passthrough charging – the ability to charge both your phone/tablet and itself at once. It does at least support auto-on/-off, with no fiddly buttons to press to start or stop charging,and no power wasted once the attached device’s battery is full.  Unlike rival power banks the Vinsic 20,000mAh Power Bank is not supplied with a soft carry case, although we don’t think it particularly requires one. Neither does it have a built-in LED flashlight, although a device of this size will not make an ideal torch in any case.  In terms of its capacity to price ratio, the Vinsic doesn’t offer as good value as the EasyAcc PowerBank PB18000. However, we prefer its design and the digital display and auto-on/off functionality win it extra Brownie points. Also see:  Best desktop chargers 2015.  Follow Marie Brewis on  Twitter. 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.