I think you will find that a lot of people are only turning on 4G when they have some serious surfing to do. Otherwise they leave the phone on 3G. In other words if you don't immediately need the extra speed don't pay the battery draining price for it. YMMV!!
Good luck.
I have 4G on all day plus GPS. In fact, I just put it on the charger after 13 hours and still have 50%. If I kept it off, I could easily get another 3-4 hours of medium to heavy constant use on wifi.
My average day is about:
(10) 10 min. phone calls
(1) 30-40 min phone call
10 texts
1 1/2 - 2 hours browsing
Twitter and facebook updates all day
60 emails
2 hours of games (right now, it's Monopoly)
From 5:00 pm on, it's on wifi with GPS and bluetooth off.
The key is understanding smart actions. Before I started using them, I was lucky to last to 20% in 8 hours. Taking 30 mins. to set them up according to my schedule nearly doubled my battery life. If it hadn't, I would have returned the phone and saved my upgrade.
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