It would be nice if the HTC ThunderBolt had a widget or an app that would easily let you toggle between 3G and 4G. When I'm on 4G, my battery drains really quickly, even if I'm not actively using the phone. I could stop all my background processes, but that doesn't seem like it's the best option for me.
Here's how you can manually switch between 3G and 4G on your ThunderBolt:
Open the phone dialer
You'll see a menu titled "Testing"
Go to "Phone information"
Scroll down until you see "CDMA + LTE/EvDo auto"
To set your ThunderBolt to stay on 3G, select: "CDMA auto (PRL)"
Then, when you want to go back to 4G, select: "CDMA + LTE/EvDo auto"
It's a tedious method, but it's not nearly as sophisticated as hacking your phone, rooting your phone, or loading any custom ROMs (no need to start your phone in bootloader mode). I'm hoping that the next software update from Verizon will allow users to easily switch between 3G and 4G.
It's great to have 4G speeds, but I wouldn't want to use my phone on 4G unless I had an extended battery, a backup battery, or some other power source.