Practical, easy to assemble and immediately operational on my GoPro HD HERO 2. Autonomy is a priori doubled even though I have not been able to test in conditions. A must for who wants to achieve long video without taking the head with autonomy, can serve as an independent charger needed .. I take off a star for the price, too high (like many GoPro accessories) for what remains a simple plastic case cell made in China.
