I recently found my iPhone 4 running out of battery power in the middle of the day. The problem kept getting worse, which led me to believe the battery wasy giving out (the phone is a year and a half old, so that made sense).
Turns out the problem was my email settings. I have a couple of accounts, so my problem may be more acute than for most people. Still here is the fix, which was nothing short of miraculous.
Turn off push mail: If you have a push mail account such as Yahoo!, MobileMe or Microsoft Exchange, turn off push mail. You don’t need it.
Go to Settings > Mail, Contacts, Calendar > Fetch New Data > Advanced. There you will see a list of all of your email accounts (if you have more than one, or just one if that’s all you have). Set each email account to FETCH. then pick how often you want the phone to fetch new email. I set mine to every hour and that’s plenty of email input for me.
If you need to get emails more often you can pick 30 or 15 minutes. Bottom line: don’t use ‘push’ unless you truly need to get email immediately throughout the day. If that’s the case be prepared to suffer from poor battery performance.
For more battery saving iPhone tips click here.