I can only speak from personal experience with genuine batteries versus cheap knock offs Stefan- you do get what you pay for to some extent. I have had a few cheap ones over the years but they have always under performed versus the real deal. I currently have six LP-E6 batteries (five genuine and one cheap one I inherited with another camera). I don't even bother using the cheap one anymore. Lasts about half as long on any given night versus the others.
You will find you can get non Canon batteries even cheaper if you go online so the question becomes- is it worth spending up to quadruple the money on a genuine battery for maybe a 25-50% gain in longevity? Maybe not, if you are using them as spares, but if it turns into your sole battery for a key project then I for one would not trust them.
If you look around online a bit you can even come across genuine Canon batteries for much less than you will find in store in Australia as long as you are prepared to wait for shipping.
For example:
http://www.ebay.com.au/itm/NEW-Origi...item3f3a8ffe95