I was in a fringe area and 4G simply wasn't working at all and the phone refused to automatically switch to 3G. So, I forced it into 3G using the following method:
Go to phone and dial: *#*#4636#*#* (same as *#*#INFO#*#*)
Then, tap on "Phone Info".
Then, click on "CDMA + LTE/EvDo auto" and change it to "EvDo only".
NOTE: WHEN YOU REBOOT, THIS DOES NOT REVERT BACK. YOU MUST CHANGE THIS BACK MANUALLY. PLEASE DON'T COMPLAIN THAT 4G DOESN"T WORK AFTER YOU FORCE TO EvDo
Later on when you want to bring up this app, you can just select "Testing" from the recent apps menu (hold Home button).
Click on Battery Info to see exact battery percentage remaining.