Ok, I am buried with changing companies, so I will be very brief on this subject
WiFi ON with Ask to Join Networks ON: iPhone will scan for new WiFi points every 60 seconds while it is UNLOCKED ONLY and not actively connected to a WiFi point.
WiFi ON with Ask to Join Networks OFF: iPhone will scan for known WiFi points AT UNLOCK based on LOCATION and will continue to check for a KNOWN point based on your current LOCATION until connected.
WiFi will AUTO DISCONNECT within 60 seconds upon iPhone going to sleep UNLESS there is an active connection and the application makes an API call to keep it alive. Currently Apple's SDK documents that connection will only stay active for up to 30 minutes unless it re-request another block of time.
Now what does this mean? If you run a test of "WiFi On with Join Networks OFF" at or even NEAR a location where you have TAUGHT your iPhone that a TRUSTED WiFi point exists but that WiFi point is OFF, OF COURSE you are going to drain the battery FASTER. This is a NO DUH moment if it ever existed. This why location data is collected and used by Apple. It is to SAVE BATTERY life for the cellular radio, WiFi radio and full positional (sub 100 meters) GPS locking.
But if you change the condition without reteaching the iPhone, you can bet your life you are going to drain the battery.
So if you are in a location with NO KNOWN WiFI points and you have WiFi ON and Ask to Join Networks OFF you will NOT drain your battery. PERIOD. End of that myth.
WiFi ON with Ask to Join Networks ON: iPhone will scan for new WiFi points every 60 seconds while it is UNLOCKED ONLY and not actively connected to a WiFi point.
WiFi ON with Ask to Join Networks OFF: iPhone will scan for known WiFi points AT UNLOCK based on LOCATION and will continue to check for a KNOWN point based on your current LOCATION until connected.
WiFi will AUTO DISCONNECT within 60 seconds upon iPhone going to sleep UNLESS there is an active connection and the application makes an API call to keep it alive. Currently Apple's SDK documents that connection will only stay active for up to 30 minutes unless it re-request another block of time.
Now what does this mean? If you run a test of "WiFi On with Join Networks OFF" at or even NEAR a location where you have TAUGHT your iPhone that a TRUSTED WiFi point exists but that WiFi point is OFF, OF COURSE you are going to drain the battery FASTER. This is a NO DUH moment if it ever existed. This why location data is collected and used by Apple. It is to SAVE BATTERY life for the cellular radio, WiFi radio and full positional (sub 100 meters) GPS locking.
But if you change the condition without reteaching the iPhone, you can bet your life you are going to drain the battery.
So if you are in a location with NO KNOWN WiFI points and you have WiFi ON and Ask to Join Networks OFF you will NOT drain your battery. PERIOD. End of that myth.