Battery life is usually the first thing to suffer when using more data than usual. The Thunderbolt's spiritual predecessor, the Evo 4G, had notoriously abysmal battery life, and while the Thunderbolt's isn't quite that bad, it's definitely less than we'd like. The problem seems to stem from the fact that it's not possible (at least, I couldn't figure out how) to manually switch to 3G to conserve battery life. That forces the Thunderbolt to use 4G at all times, which is nice and fast, but pretty tough on the battery. My tests aren't scientific, but in daily use, I found my Thunderbolt needing a recharge by mid-evening. If you're very careful, using minimal screen brightness, turning off Wi-Fi and GPS, forgoing battery-killing activities like streaming music or watching videos, I'm sure you could make it through a whole day--but what's the point of that? This is a supercharged phone; I want it to be as impressive as it possibly can be, all the time.