no, the GPS antenna is not a huge battery drain.
applications that USE the gps antenna, and keeping the screen on full bright, are very big battery users though.
make sure you are using OFFLINE maps, and nothing like traffic or other online data, and the battery will last a long long time.
i currently use gps applications on android and the battery will last for over a day while tracking rides, if the screen is only automatically turned on for waypoint/navigation . with the screen on constantly, it will only last about 12 hours.
find out what is using your gps, and you'll find out what is killing the battery by constantly doing calculations.