NV4200GO, DELL Latitude D800, Linux, Power consumption

[vlk]

WHY windows run 6hours and linux only 4hours on fully charged batteries?
on my laptop i have problem with more power consumption if I install proprietary nvidia drivers (it is about 21W - cpu 0%),
with opensource nv driver is consumption little bit less (about 18W)
and in console with framebuffer is consumption about 14W
i tested power consumption in windows with original nvidia drivers and consumption is about 16W!
exist any way to drop down power consumption on computer wit nvidia driver on linux?
PS: I use legacy driver 1.0-8776 - this is latest that working on my graphic card, i tested some others and no happens.

thanks for answer.