It's logical, but I never thought about it: If you turn off equalizers, your iPod is going to consume much less than with enabled equalizers, because the equalizer effects are computed by the iPods CPU which drains battery power.
If you use EQ settings in iTunes, you have to set your iPod equalizer to "flat", because otherwise, the iTunes EQ settings for each song are going to override iPods "EQ off" settings.
More information can be found on Apple's website.