Given that the G2 phone line was only released about 6 months ago, it's hard to imagine that the replacement phone's battery was used so much that it doesn't hold a significant charge anymore. The phone is similarly configured (stock Verizon OS, rooted, a number of bloatware apps removed), so I can't imagine why the battery life is so much worse. Had I not experienced such good battery performance with my first phone, I perhaps wouldn't mind so much. But this one is definitely a let-down.
What could possibly cause such a difference in battery life between my two instances of the same model phone? If my replacement phone does indeed have a defective battery, I'm suspicious whether I'd be able to get another replacement just because the current one isn't as good as my old one. Is perhaps the quality control on the G2 battery low enough that you might by luck get a good one or a bad one, and I was lucky with my first one and unlucky with my replacement?