Actually, your Blackberry will use less power when it is connected to a 3G signal. Where a phone uses excess battery power is when it switches back and forth from a 1x or 1X signal trying to lock into a 3G signal. Your phone was designed to use the 3G network of Verizon Wireless. The 2G signal you are probably seeing when your phone scans the network bands is AT&T's signal. It is not compatible with your device, so it will not connect. Where you can connect to 2G signals is when you are overseas, like in Europe. If your phone is not locking into a good 3G signal, I suggest you first, make sure you are running the latest software for your device. In your case, the Bold 9650 runs 188.8.131.522. Next, try updating your phone's PRL by dialing *228 and selecting Option 2 when prompted. It takes about a minute and is a free call. Then, pull your battery and allow your device to reboot. After you are back up and running, see if your battery performace is not a little better. Other things you can do is turn off WiFi, when not in use and turn off your Bluetooth signal when not in use. WiFi and Bluetooth will eat up a battery. I hope this all helps.
Are you running any third party apps or themes?