The following is my reply to a question regarding battery life with Optimus (it is the 7th post in that thread:
I find that there is no difference with either the GT 550m switched on or off. In two of the eight tests I managed to get a little over 4 hours. Once with the GT 550m on and once with the GT 550m switched off; i.e. using the Intel HD 3000 graphics core.
The problem is not the energy drain, but the size of the battery. My IBM Thinkpad T40 and Lenovo IdeaPad Y470 both comes with a 6 cell battery, however, the battery that comes with the IdeaPad feels about 20% lighter than the ThinkPad's battery.
Measuring power consumption under typical usage with a Kill-A-Watt meter, I measured between 13w - 20w. Generally it would spike up to 20w while watching a Youtube video, but drop back down to 17w/18w while the video is playing. Note that actual power consumption would be a little less since the laptop's power brick is not 100% efficient.
Assuming the power brick is 80% power efficient, that means actual power consumption would probably be roughly 10w - 16w.