Achieving All-Day Battery

iOS 9

per-app battery usage low power mode environmental factors inteligent suggestions

Xcode

iOS energy gauge

• CPU
• Networking
• Location
• Background Location instrument

Energy = Power x time

use lesser Power -> lengthen the usage time

• Eliminate polling and timers
• Response to user action and being idle
• Do the work later and allow delay
• Batch work

Networking -

• beware high,fixed power costs
• Design it by using minimal cost
• try to coalesced -- group the networking together and not to do long networking
• Background update and use NSURLSession
• use notification sparingly

Location -

• Don't keep updating location unless need to
• invoke startUpdatingLocation() when need to
• call stopUpdatingLocation() asap
• use requestLocation() in iOS 9 for a quick grab of user's location
• locationManager.allowsBackgroundLocationUpdates = false to make sure the background locational update is not performed
• lower accuracy saves power
• set alowDeferredLocationUpdateUntilTraveled:timeout: to give tolerance for system to perform location update while saving power

Background operation - Don't delay "real" sleep

• startBackgroundTask() keeps device awake
• only start for non-trivial user work
• call endBackgroundTask() asap