I am sitting at the airport browsing with blazing 4G speeds. When I am using my HTC ThunderBolt on 4G mode, I make sure to carry a spare battery supply. I like having the option to switch between 3G and 4G so that I can conserve battery life.
Eventually, I am sure that we will find a way to improve battery life when we are connected on a 4G network. Until that happens, I will use my external battery charger.