Suppose you have two identical ultrabooks but one uses dedicated graphics instead of using the one in the CPU, if you execute the same office tasks on both machoines (i.e., not gaming) will the battery life of the Ultrabook with dedicated graphics perform noticably worse?
Most notebooks new enough to have a processor with integrated video use GPU switching to power down the discrete GPU during trivial use. In those cases, there is almost no power penalty for having a dGPU.
This switching solutions make the drivers more complicated, however, and so you may find that you need to disable switching and force the dGPU enabled. In that case your battery life would suffer considerably. (Consider that GPU switching is a complicated technology -- no one would use it unless there was a big power savings)