A dual-output 6000mAh power bank such as this Sandberg is ideal if you’re on the road and have multiple devices to charge – just don’t expect to do so more than once.   With 6,000mAh of power and an average 70 percent efficiency rate for most power banks, you can expect around 4,200mAh to be available for your mobile devices. That may be enough to charge your phone twice if its own battery isn’t too capacious (ruling out many Android phones), but don’t expect enough power to also fully charge a phone and a tablet. Also see:  How to improve smartphone battery life.  The low capacity does have a crucial benefit, though: portability. At 156g you won’t notice this power bank slung in a bag, although in your pocket it would feel as though you were carrying a second phone.  Also see: Best MiFi 2016. The 10.5W USB output will come in handy if you do want to connect a tablet, and you may find your phone will also charge faster from this connection – many smartphones these days support higher than 5W input. You can connect your phone to either port and, with a max output of 15.5W, you can actually use both ports at once. Also see:  How to charge your phone or tablet faster.  On hooking up our HTC Desire Eye we were disappointed to find the Sandberg doesn’t support auto-on or -off. To begin charging you must press the black triangle in the top corner. Below this are four LEDs, which glow blue to show you how much power remains. We’d much prefer to see an LCD in a power bank, but at this capacity one isn’t necessary.  Perhaps the lack of auto-on/off support shouldn’t have come as a great surprise, mind, since there is nothing here in the way of extra features. The Sandberg doesn’t support passthrough charging – you must first charge it, which can take up to seven hours over the 5W Micro-USB input (a cable but no charger is supplied), and then use it to charge your phone or tablet. It doesn’t even feature an LED flashlight or come with a carry case.  The design isn’t such that you feel you need to protect the Sandberg Powerbank 6000, of course. It has a very old-school-looking rectangular design, and reminds us a little of a cheap Mi-Fi router or remote control. Built entirely from plastic, the blocky design with sloping edges feels comfortable in the hand but doesn’t look particularly inspiring. 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.