5 Customize Your Mail Settings
Although this depends on your individual circumstances, most of us don’t need our iPhones to constantly monitor our email accounts for new messages. For those of us who don’t, Push and Fetch email are both pretty big battery drainers.
If you don’t need to check your email much, it’s best to go to Settings > Mail, and set Fetch to manual — that way, you’ll only receive new messages when you actually open the app. You can set it to a longer interval if you need it, or set it to Push. On that last option, there are conflicting views about whether or not it saves battery life, so weigh your email-receiving preferences with your battery life needs to find the best fit.