How do you switch from 4G to 3G on the Sensation? a few of my co-workers have several different HTC models with different carriers among them, and they all have a widget to switch on/off their 4G. Can bear to keep this phone any longer. Otherwise, all other connections (wi-fi, etc.) are all off, auto-sync off. What else could be draining my battery in a matter of about 4 hours.
You could try doing a reset to be sure that you don't have anything running in the background you are not aware of. If you have any map program or anything that hits the network a lot will suck up the juice.
Forgot to answer your original question. You can switch to GSM mode to reduce power consumption.
From the home screen > Settings button > settings > Wireless & Networks > Mobile Networks > Network Mode > GSM Only
This will put you into GSM mode only but your phone should last most of the day at least. You don't have it powering your coffee maker do you :) When you run apps they often don't exist but continute to run in the background. If you have ran an app like a Maps one, they poll the network and GPS all the time which eats up your battery. One thing I try to do is use the [back arrow] to exit a program. Just keep punching back until you get to the home screen. That will usually force the app to actually exit. Another thing to do is power off the phone and then power it on occasionally. The power cycle will typically shut down all programs that don't start at boot and clear out memory. You can also go to what is using battery and see what is listed. Keep in mind that it lists everything since the last power cycle and so you really need to power cycle the phone to get a known starting point.
On T-Mobile 4g and 3g are on the same band(s), so you don't switch between them. (The 4g indicator lights up when it connects to either one which is, understandably, confusing.) However, as TheFlowGuy said, you can switch between 3/4g and 2g (EDGE) which will use less power by changing the Network Mode to GSM Only. That should be fine for updating e-mail, Twitter, weather and Facebook in the background.
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