For two years I've been carrying a small Kensington Ultra Portable Battery Pack so I can give my iPhone a juiceboost during the day. When new this battery would provide nearly two full charges to the phone and it has worked perfectly. In fact, it is still going strong. On the debit side, the unit needs both an external iPhone cable and a separate mini USB cable for charging.
Today, however I came across the Hypermac Nano in a local store (Micro Anvika) and was immediately attracted by the brand because I've heard such good reports about Hypermac's external batteries for MacBooks. Having seen the battery pack on Amazon at over £59.99, I grabbed on of these off the shelf at only £39.99. Bargain.
This little device is a model of good design and convenience. The Nano charges from an iPhone cable, so no second charging cable needed) and has a neat tethered iPhone plug which slots into the device under the removable cap (which, incidentally, clips magnetically to the bottom of the Nano so you don't lose it). Because the connectors are both iPhone compatible, the unit offers pass-through charging of both battery pack and iPhone at the same time. Capacity is a surprisingly high at 1800mAh (exactly the same as my old Kensington unit) and Hypermac claim one and a half charges of the iPhone.
It's a very compact unit measuring 9 x 3.7 x 1.3cm and can be slipped in a pocket or the corner of a bag. I have some concern is that the tethered cable connecting the battery to the iPhone plug is super thin, like a length of very thin string. I will test it over the next few months and report on any problems.