Under the network settings you access with a dialer code, you can "Set Prefered Network Type". (I have an app that directly opens to the page.) At work, my phone kills its battery switiching networks, but it is fine if i switch to "CDMA only". I have tried and failed numerous times with Tasker to automate this based on location. However, my Tasker understanding is poor at best, and I'm not even sure if this can be done. Searching has yet to yield any results regarding this function. I'm using a GS4 running CM11 if it's relevant.