I've been shooting a great number of interviews on the Canon 5D Mk III lately, and thought it might be useful to broach the subject of battery life.
Using the Canon battery LP-E6 I've been averaging just over 1hr and 30minutes of continuous shooting with the lens stabilizer on (Canon 70-200mm f4 IS). It has lasted to about 1:45 without the stabilizer on, but 1:30 seems to be the safe amount to bet for calculation.
Of course every battery has a slightly different efficiency, so erring on the side of caution is smart as you don't want your battery to die mid shot.
Chris Stenberg is a photographer, filmmaker, occasional wordsmith, and traveller. In his spare time you can find him hanging out with his family and/or biking and boarding in the mountains of British Columbia.