then read on…
first: be aware there’s a difference between “Push” (which is for some email account types & some MobileMe features) and “Push Notifications” (which is for apps). they are controlled in separate Settings screens.
short story:
if you’ve upgraded to v3.0, usually have Wifi ON, and experiencing short battery life, and if you can live without Push Notifications (at least until Apple finds a better solution), TRY TURNING “Push Notifications” OFF.
alternatively, if you need Push Notifications but can live without Wifi, try turning Wifi off & let the data travel via 3G.
long story:
first I ran alternate days with Wifi ON, then Wifi OFF, and noticed with Wifi OFF my battery life was nowhere near as short (I could get through a day), but with Wifi ON, I can barely get through half a day. this is very different to v2.21, and in my setup the only significant difference was Push Notifications being ON.
so today i’ve been running continuous pings from my Mac to my iPhone, with various combinations of Push on/off, Push Notifications on/off, email accounts on push / fetch / manual, and discovered there’s a huge difference in how often Wifi gets turned on when Push Notifications is enabled.
with Push Notifications ON, while your iPhone 3G (and probably 3GS) is asleep, Wifi will be turned on for 15-20seconds every 1 to 2 minutes!
this is in stark contrast to Push Notifications OFF, but Push (for email, MobileMe, etc) ON, where Wifi is on only as often as your email account settings dictate.
this explains a lot, I think. with Wifi OFF, data goes through the 2G/3G radio, which is inherently ON all the time (for phone functionality), so the incremental ‘cost’ (to battery life) of Push Notifications is comparatively small.
but with Wifi enabled, data is instead sent via Wifi. the incremental cost (to battery life) is dramatically higher having to turn on the Wifi radio, find the WLAN, get an IP from DHCP, then exchange data with various Internet servers, when it happens every couple of minutes!
though I’m not really sure what Apple can do about this situation. they appear to be turning Wifi on frequently to give the illusion of true (ie timely) push notifications. i think this situation runs parallel to those who found, with v2.x, that enabling Push on email accounts & Wifi enabled had similar major negative impact on battery life. except now heaps more people want the Push Notification feature. interesting conundrum…
