Ever since getting my HTC Thunderbolt 4G I've been battling to figure out ways to extend my battery life. I've covered a number of those issues and alleged solutions here, including: Juice Defender and turning off 4G. Both are pretty effective, but when you have a fast processer in a tiny phone it's still gonna suck the power quickly.
The most effective thing to do is simply change your Smartphone lifestyle and keep a charger with you everywhere you go. Even so, you might find yourself out of juice. In that case I strongly recommend getting a Duracell Instant USB Charger with Lithium ion battery / includes universal cable with USB and mini USB, or another such device. That way you don't need any other power source.
Another way to help your battery hang in there longer according to some "experts" is to calibrate your battery on a monthly basis. I'm not sure if it's effective yet, but it's worth a try. Here's what you do:
1) Turn your phone ON, charge it until fully charged (the light turns green, or goes off, or whatever your phone does).
2) Unplug your phone from the charger and turn it OFF. Immediately plug it back in (with the phone OFF) and charge it to full charge again. This usually takes less than one hour.
3) Unplug your phone and turn it ON. Once it is fully booted, wait two minutes and turn it OFF.
4) Plug it back in, charge until fully charged again. (Again, it won't take too long.)
5) Unplug the phone, turn it ON and see how things work out.
Let me know how it works for you.