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I'm looking at the 'turn on near my favourite places' functionality, and wondering whether it is really going to save battery.
Which takes more energy? Scanning for wifi, or running geofencing and Cortana in the background?
Also, does Cortana perform properly for this if internet is turned off? Currently for most things that I ask Cortana when offline it just says "Sorry, no internet at the moment, try later".
When you select the option "turn on near my favorite places", your phone will monitor for geofences(your favourite places). Geofences tells apps to trigger some experience for you when your phone enters or leaves them. In this case, it tells the WiFi, to switch on and the WiFi starts scanning for available networks. It definitely saves your battery, because if you are WiFi is switched on all the time, it is likely to search for WiFi networks most of the time thus decreasing your battery life. But with geofences it turns on and searches for WiFi Networks when you are at your favorite places like your home, work, etc.
Cortana doesn't work well without the internet, in fact she doesn't work at all without an internet connection. The only thing she can do without the internet is give you reminders including location based reminders. Since location based reminders work on GeoFences, it triggers Cortana to remind you about your reminder at the place you have told Cortana to remind you.
More information on GeoFences can be found at http://www.windowsphone.com/en-in/how-to/wp8/apps/location-awareness-and-my-phone
I have to say that I don't use geofencing because it drains the battery far too quickly. I do however leave my wifi on the whole time, and do not get significant battery drain from it. Doubltess I would get better battery life if I left wifi off too, but leaving on it on has generally not caused me too much concern.
On my Lumia 1020, using geofencing is a non-starter for this reason. From my own experience, on my old Nokia N8 and Lumia 1020, any use of GPS (which geofencing by its nature will use) is the single biggest source of battery drain on the phone. In my case, I found that using geofencing to determine whether to enable wifi will drain my battery far faster than simply leaving wifi on but turning geofencing off. Obviously results may differ with your own phone, and your own usage.
Also, when I first tried Cortana on my Lumia 1020, I found that my phone had use up as much battery by lunchtime as it had previously used by about 5pm. When I turned off location services, the problem went away but then I could no longer access Cortana. So my middle ground, which works for me, is to enable Location services, but turn off geofencing. Cortana now works for everything other than those things that require geofences (and to be honest I didn't find them particularly useful anyhow) and I still have a usable phone by the evening commute.
