I don't consider that my phone has battery issues. My battery lasts at least 1 day under what I consider normal use (what you guys would consider light). Good enough for me.
Now if I start flashing roms, creating and restoring backups for a little while, yeah, that's another story!
I can't understand why they would give you a new phone, though. Imagine if it's the same for cars? I buy a brand new car, after a few months, the battery dies, I bring it to the dealership and they say "Yeah, defective battery. You need a new car".