It's a few months later now, and I've finally got myself an external battery device.
I recently bought a new Android phone and I knew before I got it that I would probably struggle with battery life (it's not too bad for a low-use user like me, but it really could do with a better battery than 1500mAh).
With this in mind, I've been looking at external battery devices in case I get caught out anywhere or if there's a power failure at home (it has been known!).
I decided on the iAnker Astro 3:
For around £30, you get a 10,000mAh battery with two USB ports (5V,2A) plus an output port switchable between 9V and 12V for charging larger devices such as cameras, netbooks, tablets, etc. One of the USB ports is "designed for Apple" products and the other "designed for Samsung". I'm not sure of the difference.
I've had it for a few days and have successfully used it to charge up my new phone and iPad simultaneously. I don't yet have the correct tip for my Android tablet, but I should have one soon. Many charging tips are provided, but not the one I need.
This isn't rugged like the Mophie of the original review but, at a third of the cost, that's understandable.
The weight of the Astro3 means it's not something you'd be comfortable lugging around in your pocket every day but they do smaller versions (2600mAh, 3200mAh, 5600mAh, and 8400mAh). I'm pleased enough with the Astro3 to consider investing in one of the smaller more-pocketable devices too (starting from under £15 for the 3200mAh version). I know others who are often short of battery power when away from a mains socket, so I'll probably be getting some of the smaller ones in for Christmas presents.
There are so many of these devices around that it would be nice if there was a good comparison review of them. Looking for sensible reviews on the web is an exercise in difficulty.