One of the perks of buying a Zendure power bank is the higher than standard efficiency of 80 percent. This means of the 13,400mAh advertised capacity you’ll see some 10,720mAh, whereas rival power banks might offer only 8,700mAh.This will charge any iPhone between five and six times, and an Android phone between three and four charges, depending on its battery capacity. By comparison your take-home figure on the Zendure A3 is around 8000mAh. It measures 96x62x24mm and weighs in at 224g, while this higher-capacity Zendure A4 is around 108x72x24mm and 260g. It’s not a huge difference, but it is a difference nonetheless when you’re talking about devices designed to be portable. In both cases Zendure has done a great job of cramming in so much capacity into such a small case, while keeping down the weight and size to a reasonable amount. See all power bank reviews Not only do both models offer high efficiency, but they can also maintain this power longer. Pick up one of these power banks six months later and it will still be as full as it was the day you last used it. These are two of several in the Zendure A family, which starts with the 6,700mAh Zendure A2. In our opinion, the A2 is one of the best all-round power banks money can buy. At the top end is the Zendure A8 QC, which is ultra-high in capacity and builds in the latest technology, such as Quick Charge 3.0. Sitting in between and borrowing some features of both are the 10,000mAh Zendure A3, the 13,400mAh Zendure A4 (reviewed here), and the 16,750mAh Zendure A5. All models in the A Series have the same design, which utilises a very tough, crushproof PC/ABS composite material with dual-injection molding and a shock-absorbing central belt. They stand out among a sea of boring black plastic power banks. Note that only the top A8 QC has an LCD screen, and those below it – including this model – use four LEDs to show how much capacity remains. Also see: How to charge your phone’s battery faster  When the battery is depleted it can be recharged in as little as nine hours over its 1.5A (7.5W) Micro-USB port, and one of the neat things about this device is it supports passthrough charging, which means it will charge its own battery at the same time as any connected devices, without causing any harm to the hardware. If you have few spare electrical outlets handy this can be a lifesaver. Where the Zendure A3 and Zendure A4 differ from the A2 is in its capacity, obviously, but also the number of outputs. However, it’s worth pointing out that while you get an extra USB output here, the max total output isn’t any higher: the A4 can offer 2.1A (10.5W) from one USB output or shared between two. Nevertheless, not all the devices you plug in will want to draw the full charge available, and to aid in divvying up the power there’s Zen+. This is clever device-recognition technology that delivers the optimum charge, rather than firing out the full amount and leaving it to your device to take only what it requires. Also see: How to improve smartphone battery life Operation is plug and play, so you simply plug in a USB cable and connect your mobile device to begin charging. The power button is used only to see how much power remains in the bank. There are features this power bank doesn’t provide. For example, there’s no LCD screen, and no support for USB-C or Quick Charge 3.0. However, the four LEDs lined up above the power button do a reasonable job of inferring how much power remains in the bank (each represents 25 percent of the total capacity, so 2,500mAh), and USB-C and Quick Charge 3.0 are useful only for those with the most recent flagship phones. As it stands, the 10.5W output it does offer is fairly nippy. 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.