To test the battery today we put the machine through three sets of real world situations.
One as a media movie lover on the move, a person wanting to watch HD media on a train journey or bus with two thirds screen brightness (any less and quality suffers).
Secondly as a business man, using the machine for productivity with wireless enabled and balanced power settings with a mid way (around half) brightness setting.
Thirdly as a gamer on the move, with screen brightness up high.
We are testing with the optional external battery disconnected, then connected.
Battery life is fantastic, although our results fell short of Sony's claims – which are ‘up to' 7 hours with single battery, and ‘up to' 14 hours with dual battery. Perhaps if you used the Z Series with everything disabled and brightness down very low, it may be possible. These aren't realistic conditions however. Still, excellent results and with the extra external battery, realistic ‘all day' life is possible.
An added benefit with the external battery added, is that the heat from the underside of the Z series laptop won't make contact with your skin or clothes.