Dave Dugdale from Learning DSLR Video wanted to know, and put a genuine Canon LP-E6 battery vs a Watson LP-E6. He found that the Watson must have a chip built in since the 5D Mark III can register it and track the performance. Contrary to the Canon manual saying you can recharge whenever you want, the Watson manual says to recharge only when the battery is dead. This could mean that the Watson battery has less charging cycles.
In his tests a new Watson LP-E6 lasted 1 hour and 9 minutes, a one year old Canon LP-E6 lasted 1 hour and 28 minutes. Consider that the Watson is about half the price of the Canon (or even less).
What’s your experience? Are you using third party batteries (I do)? However, be aware of counterfeit batteries: Canon has a page dedicated to this issue.