I just recently switched from ATT to Verizon and I find my Verizon Project (RED) iPhone 7 battery last a lot longer than my Jet Black iPhone 7. Where I live and work reception is not an issue - usually full bars the entire time. Where my ATT phone would be almost drained by the time I get home around 7p (off charger 7a), my Verizon iPhone 7 still has 40-50% left. Needless to say, I'm very happy.
Did you set up the red iPhone as new?