The GoPro HD Hero 3 series cams are performing excellent in many aspects, except battery lifetime. At least for surface use I've come across something that helps in those cases where you drained all your spare Hero batteries and still want to shot more footage: a comparably small USB battery tank with quite some capacity. It is perfect to give your GoPro HD Heros some more juice, as well as to your mobile phone.
There are now more and more manufacturers and different kinds of USB battery tanks poping up everywhere as these reserve batteries gain more popularity. Depending on your needs and pocket money you can choose over a wide range of battery capacities as well as connector types: ordinary connectors and different. For those with an Apple-Lock-in there are those devices available that come with the corresponding different proprietary connectors.
When strolling the local electronics chain store Conrad, I got myself an 8Ah battery tank of type Power Cube 8000M under the brand of MiPow. This little orange box delivers up to 2.1A in total through it two standard USB connectors: one being an integrated cable ending in an ordinary microUSB connector, the other one being the usual ordinary type A connector. The latter is perfect for connecting the USB connector cable to which came with your GoPro HD Hero. Well, don't for forget to take this cable with you, as GoPro decided to go for the miniUSB connector instead of the now more commonly found microUSB connector.
|MiPow Power Cube 8000M|
You charge the glaringly colored box itself also using USB, in this case you can use the separate microUSB cable that came with it. Use any USB charger you want. For best performance you should use a 2A or 2.1A USB charger as the orange box can slurp up to 2.1A if available. It takes quite some time to charge the USB tank but this treats the LiPo battery with care and keep things cool. Personally, I'm using a USB charger sold under the brand name Hama; for instance, the big Samsung USB chargers can also deliver 2A.
MiPow notes in the accompanying leaflet that you may be unable to use up to 20% capacity. This probably has to do with the way the whole USB charging procedure works: the LiPo battery inside the orange box operates at 3.7V, which have to be stepped up to 5V in order to load your USB device. Inside the GoPro HD Hero or your mobile phone the internal charging unit will step down to 3.7V again. This doesn't work without losses.