If your iPhone battery is getting low and you aren't near a charger, or going to be near one, for a while, then there is an option you can choose which puts your iPhone into a low power mode. This means it will use less battery power, background activity will automatically be reduced and your phone will therefore last longer!
Step 1 - Go to 'Settings' in your iPhone.
Step 2 - Scroll down until you see 'Battery' and go into this setting. It should have a small green and white battery icon next to it.
Step 3 - Tap the slider so that 'Low Power Mode' is on. If you don't currently have the percentage showing for your battery, then this will be visible as soon as low power mode is on. The battery icon in the top right corner should also turn yellow.
Step 4 - Use your phone sparingly. Your battery should now last a lot longer. Once you are able to charge simply follow the same steps to turn low power mode off. Or it will be automatically deactivated once your phone has enough charge.