[jyl]

I've occasionally noticed my phone getting warm and the battery draining. A full power off (hold both buttons until phone turns itself off, wait a couple minutes, then turn phone on and let it reboot) usually kills whatever was running amuck.

Otherwise, time to optimize battery consumption
- In mail, turn off fetch, use push
- Turn screen brightness to middle
- Turn off notifications you don't use
- Turn off location services you don't use
- Shut down any app using GPS, if you're not using it
- Disable background updating for apps that don't need it
- Go to battery in settings, see what is using the most battery

You might want to consider upgrading to the new iPhone SE when it is available end of March. Same compact size as your iPhone 4, all up to date internals (like iPhone 6S), $399 for 16 GB version.