Theis one of the first 4G LTE phones available on the Verizon Wireless network and, as we've seen in our review, its download speeds are superfast. However, as users are starting to note, you'll pay for that speed with abysmal battery life. This is even more frustrating for users who operate in areas where 4G hasn't yet been rolled out. Unfortunately, it would seem that there is no obvious way to toggle between the Thunderbolt's juice-sapping 4G mode and its more battery-friendly 3G antenna. There is, however, a hidden menu that will let you do just that.
From your Thunderbolt's dialer, key in "*#*#4636#*#*" and you'll be taken to a hidden test menu that features an array of secret options and statistics for your handset. Tap the first heading labeled "Phone Information" and scroll to a drop-down menu labeled "Set preferred network type." Here is where you'll be able to select how your phone connects to Verizon's network.
The default setting is "CDMA + LTE/EvDo auto," which allows your handset's software to automatically decide between the 3G and 4G antennas for the best possible speed. If you want to stretch your battery, then you can select the "CDMA auto (PRL)" option from this menu to lock your phone into 3G mode. Anecdotal reports from around the Web report upwards of a four-fold increase in battery life for the Thunderbolt with 4G disabled. Depending on your usage, that could mean the difference in making it through the day on a charge and being saddled with a dead battery.
When you're ready to go back to 4G speeds (and battery life), simply repeat the process and reselect the "CDMA + LTE/EvDo auto" option from the drop-down menu. The Testing menu is also home to much more interesting information about your handset, including detailed battery information, extended battery history, and an extended processor usage log that shows what apps are using the most resources.
Update: It has come to our attention that of the 4G-deactivated modes available the "EvDo only" mode previously recommended disables standard phone calls. Consequently, we've changed our recommendation to the "CDMA auto (PRL)" mode and updated the article.
(Source: Android Central)