We previously noted that although many iPhone users experience better battery life after the iOS 4.0 update, a number of users have reported decreased battery life after updating. We previously noted a number of fixes for short battery life, including removal of problematic apps, turning off Push, closing extraneous Safari windows and more.
It now appears that overactive location services usage can result in poor battery life. Specifically, apps that use location services in the background can quickly drain the battery.
To check location services usage on an app-by-app basis, navigate to Settings > General > Location Services. Turn location services off for all applications, then turn them back on for desired apps one by one or in groups. Via this procedure, you can identify which app’s use of location services is draining battery. Alternatively, you can temporarily turn off location services altogether and check for increased battery life.