I have this pet peeve of people giving bad advice about technology. The number one is how to optimize battery life, specifically the iPhone.
I saw one article that even recommended turning off wifi to improve battery life. While conceptually true, in real world practice, absolutely false.
With the iPhone 6 and 6 plus, battery life has never been better. However there are a few things I do to optimize my battery life.
Turn down the screen brightness
This one seems obvious, but a screen emitting brightness (energy) uses more energy. I keep mine at about 20% brightness with auto brightness control on. This way it gives me what I need if I'm in direct sun light but then backs down when I'm not.
Use WiFi whenever possible
At home and work, stay connected to WiFi. Not only will your connection speed likely be faster on WiFi, you won't be using the Cellular Radio unless you take a phone call (which will soon change hopefully). The cellular radio drains the battery, especially if you are in a poor signal area.
Be smart with location access
Only enable location services for apps that actually need it. In practice, I keep location services on for most apps, as I don't use most apps frequently. However, if an app keeps monitoring location and I feel it doesn't need it, I just turn off location access for that app.
What doesn't impact Battery Life
- Push Notifications - Unless you're getting dozens a minute, there wont be much impact. All that is being sent to your phone is less than 1kb. All of this is moot if you're on WiFi.
- Bluetooth - If you're not connected to anything, the amount of energy your phone is using for Bluetooth is pretty small. Even with streaming music, newer iterations of Bluetooth chipsets have become fairly good at minimizing energy usage. Conceptually yes, it does impact battery life, but not in a meaningful way if you charge your phone every day.
In the end, just think in terms of energy in vs energy out. Your screen emits energy, your phone's cellular radio emits energy, and other radios emit energy (GPS, wifi, bluetooth). Basically, you just need to optimize which energy sources are used. The screen, cellular radio (3G in particular), GPS are the biggest offenders so focus your efforts there. After that, quit worrying about it.