OK is it just my area?

when I have 4g on battery dies pretty fast.when I put it in 3g only mode my phone last all day.
 
Likely depends on the area. My area is notoriously weak on 3G but decent on 4G; whichever it has more trouble locking onto/searching for will likely drain the battery faster.
 
In N.Y., 4G seems much better for battery life than 3G. I know when my phone drains & overheats, I'm in a 3G or worse area.