How to conserve battery life for iPhone 5c overnight?

I'm a scout and I go on camps quite often. Obviously there isn't exactly an abundance of power sockets in tents, so sometimes I turn my iPhone 5c off overnight to save battery. However, when I wake up and turn it on, it has lost maybe around 30% battery life. I then leave it on the next night, with the brightness on low to see if there's any difference, and there isn't really. I've got a camp this weekend, for 3 nights, so I was wondering if anyone had any suggestions about how I can save as much battery overnight as possible, and if it is worth turning it off overnight. Also, if there's an explanation as to why 30% has been drained (it's happened on several occasions with different iPhones) that would be great too.

Are you actually turning it 100% off? (Holding power button, choosing Turn Off)
Or are you just hitting the power button once and enabling sleep mode?

Either way, go to Settings, and enable "Airplane mode".

This disables every wireless communication (Bluetooth, Wi-Fi, 3G/4G, Cellular Radio), and that'll save you the most power if you choose not to shut it off.

If you shut it completely off, the battery can't drain at all. So you probably didn't actually turn it off.

Ask the magic 8ball app.

Turning it literally off is the best solution. Honestly if it's on, it's going to drain something. But losing that much you've got something running that needs to be off. Best luck.
http://ipod.about.com/od/iphone3g/tp/iphone-battery-life.htm

http://www.zdnet.com/how-to-improve-your-iphones-battery-life-updated-for-ios7-7000014902/

Make sure you are turning the phone all the way off, requiring you to hold the power button for it to turn on to a white apple logo. IF this is true and you are still getting the battery issue, this isn't uncommon.

The software, as well as hardware that determines the battery life of an Iphone is notoriously finkicky, provides extremly inconsistant results for all iphone users I have encountered. The battery drainage is normal for batteries, as all batteries lose power over time, but 30% is excessive, and may jjust be software not detecting the battery correctly.

If you need to have your phone during the trip and working at full functionality, consider buying a large battery bank. Best Buy and other electronics stores usually carry batteries capable of one or two charges. However, if you head online, you can find some massive batteries that can charge your phone in excessive of 20 times (albeit being much larger)