The HTC One is a great phone and while the battery life is better than it's predecessor, it's nice to have some backup. So which is best, the Mophie Juice Pack or the HTC Battery Bar?
Let's start with the Mophie.
Now an established brand, particularly amongst iPhone users, the Mophie Juice Pack approach to extending the battery life on your device is to put a battery (2500mAh in this instance) inside a sleeve into which you slide your device. This has both good and bad points - it means the device is much easier to use when you're using the additional power but, well, it doesn't do a whole lot for the form factor. :)
The Mophie is nothing if not cleverly designed. Firstly it's very well made and available in a black or silver soft touch finish to complement your device (although I have a black model on my silver One). Secondly it works exactly as you'd hope! One thing that is really important is that you can charge both the pack and your phone while they are docked together. The charging is intelligent - it'll juice up your phone first, then the pack. The battery level of the pack can be checked by pressing a button on the back to illuminate up to 4 white LEDs.
To insert your phone into the pack, the top slides off. Remove top, slide in phone, replace top, job done! The pack also serves as a pretty effective protective case for your phone! There's a hole on top for the headphone port, the power button is transparent to allow the IR signal to pass through and on the bottom is the microUSB charging port as well as 4 metal pogo connectors, perhaps for some future unknown dock?
On the back is a hole for the secondary mic, a big cut out for the camera, the aforementioned button and LEDs and the main switch.
The switch is there because the pack isn't powering your phone at all times. Mophie recommend that you turn the pack on when your device battery gets low (~20%). Doing so then charges your battery - exactly how far you'll get depends on how much power your device is consuming, whether it's on / in use etc... I find that it typically tops my phone up to about 80%, which is great, although charging isn't particularly speedy (despite the output being rated a 1A).
The Mophie is a pretty unbeatable option if you want to carry on using your device while it's charging and you can live with the form factor. It's well made, effective and intelligently designed. The main downside? At £80 (silver) and £85 (black) from Amazon it's not exactly cheap.
The battery bar alternative
The alternative - admittedly cheaper / more versatile charging option for your phone - is to use an external battery bank.
These come in all sorts of shapes / sizes / capacities, but the one to have (pun intended) is the HTC 'DoubleCharge' battery bar which has a capacity of 6000Mah. It too isn't cheap at ~£45 (if you can actually get hold of one), but it is a great bit of kit.
Rectangular in shape with a two tone black / orange paint job, the battery bar - like the Mophie - has a button to show you the remaining capacity on 4 LEDs, albeit orange ones this time. Output is again 1A but with a 6000mAh capacity, you've got a good chance of getting two full charges of your device from it. The bar itself is juiced up via microUSB and includes a short USB -> microUSB for connecting to your phone. Unlike the Mophie, you can't use a single power connection to juice up both the bar and your device which feels like a considerable oversight. I like being able to plug my Mophie / phone combo into a single power connector overnight and have them both ready to rock in the morning.
In use the DoubleCharge is great... I find that it charges my phone inexplicably quickly - faster than any of my other chargers, but I can't really work out why. This means it's great for a short burst of additional power during the day when it's convenient to leave your phone charging on a desk.
And this is the main downside to the battery bar - it's rather unwieldy to use your phone while it's charging.
So which should I get?
Clearly the DoubleCharge is going to get you more power and is cheaper, but it comes at the expense of the usability of the Mophie sleeve. Think about how you're going to use it - then decide. Or give up and buy both. ;)