Judging by the other reviews, I've been unlucky. I often buy 3rd party batteries, as, even if they don't perform quite so well as the manufacturer's own, they usually work out good value.
I can live with 80% performance for less than 10% of the price.
However, there is such a thing as false economy, especially when it lets you down badly.
I bought this as a spare, for my Canon EOS 40D, for travelling in India. My Canon battery will hold charge, unused, for weeks at a time.
So, I charged both batteries before I left. I used the Canon one first, which lasted over 10 days (heavy use). I then swopped to this one - it was already showing half power and barely lasted the morning. By that time, fortunately, the Canon one was recharged. I recharged this one. And tried again. It barely lasted the day. I tried twice more with the same result.
Absolute duffer and it let me down at the worst time and place (mid of one month in rural India).
I'd give it minus stars, but can't.
I have since bought a Duracell version for a bit more - that seems to be living up to it's brand name and doing the job. I strongly suggest you spend a a few pounds more and buy the Duracell (available from Amazon).