Using the newly introduced Fused Location Provider in Android: 20 meter accuracy using GPS (5s interval) tolled 7.25%/hour, a mid-level accuracy (40m – 20 seconds) ran 0.6%/hour. Geofences require around 2.4% per day.
How does Fused work? Combining GPS, cell network location, Wifi and sensor data, as well as detected activity. Driving requires less accuracy than walking in a mall, for example. Which is also where the geofencing API comes into play, as well as the accelerometer function (for detecting walking / cycling without huge battery drain).
To achieve this, Google uses machine learning to identify the user’s activity and pulls in relevant data, which allows app developers to more efficiently use this information without directly polling the sensors themselves, which may be wasteful.