[Q] ICS x JB Battery life

Hi,

With ICS I did 2 days of batt life. With JB, even did batt calibration after installed, I get less than 1 day.

Have been trying SVA, Chrack, Cassie, and a lot more JB rom with same result... (testing for a week each one)

Why have ICS Roms so better battery results then JB?