I was wondering, I don't really need the retina screen at all, if I turned the display resolution down to just normal resolution, would that save battery life?
I watched a youtube video of a reviewer who complained about the lag on the retina model. He side loaded an application that actually allowed him to change the resolution to the normal 1400x900 resolution and said it eliminated the lag altogether. It's system optimization that creates the lag, but I don't think that would help with battery life. Maybe by 5-10% max.
I was wondering, I don't really need the retina screen at all, if I turned the display resolution down to just normal resolution, would that save battery life?
As already stated, it won't help. If you're looking for battery-saving ideas, there are many factors that impact your battery life. See the BATTERY LIFE FROM A CHARGE section of the following link for details, including tips on how to maximize your battery life.
The link below should answer most, if not all, of your battery/charging questions. If you haven't already done so, I highly recommend you take the time to read it.