IPhone battery percentage jumps?

I have an iPhone 5, I've had it for 8 months and I have no complaints about it apart from the battery life. I know many iPhone users have complained about the poor battery life and I understand their point.

However for example, today I was on 51% and just scrolling down my newsfeed on Facebook. Lowest brightness and listening to music quietly and it jumped down to 42%. It's done stuff like this before and I'm really concerned about it. I don't have any features on like location services, Bluetooth etc, but it still does this. I also have to charge it 2/3 times a day. Can someone help?

Buy an extra battery snap it in the back! This is a common issue that Apple has! Nothing can be done besides add and xtra battery power