I've purchased 2 of these Duracell E6 batteries for my Canon 7D camera, and am thoroughly happy with their performance.
I've had bad experiences with cheap imitation non-branded batteries in the past (not just for cameras, but also laptops and
xbox wireless controller batteries). They work for a couple of times, then you find they start failing to hold their charge
and then they decide they need to visit the afterlife at the worst possible moment. The situation gets exasperated if you use
poor quality batteries in cold temperatures. More often than not, the batteries fail just outside their warranty period leaving you
high and dry.
Not these Duracell babies though, they are the real McCoy and hold excellent charge when using equipment.
I highly recommend them... you will not be disappointed.