Why does my iPhone battery drain so quickly?

I have had an iPhone 4s for almost 2 years. The phone has slowed down a lot since that time and the battery is drained extremely quikly, even when I'm not doing anything. If I just listen to music for 40 mins, doing nothing else, with a locked screen, my battery will go down 20%. It's insane. I never overcharge my phone. I charge it to 100% before I go to sleep and when I wake up its around 96%

Added (1). @ WB, No, even with everything closed it, the battery still leaks.

IPhone 6 Plus or OnePlus One?

I'm trying to decide between iPhone 6 Plus or the OnePlus one, price isn't really a factor because I can afford either one. I'm just not sure what ecosystem and device I'll like more.

Which is better LG g3 or iPhone 5s?

I guess i just want an all around comparison/review of both phones.

How to get iPhone 5c on without SIM card?

We sold our daughters phone and took the SIM card out. I have to ship it tomorrow but I forgot to reset it and delete her pics.

When I try to now I can't because we only have 1 sim and that's in my husbands phone

What to do?

How much trouble can i get in for having this felony charge?

The other day a iphone was stolen in class and i happened to be blamed for it. A girl said i threatened to shoot or kill her if i snitched which never happened at all and i'm angry because my school arrested me with no proof of me having any phone and suspended me for 5 days because the girl is pressing charges. I might even get expelled because of this and goto LP or juvy. I live in LBC, any advice for me?

My recpetion at home used to be good now it sucks i don't know what to do?

So i have an iPhone connected to sprint. My reception at home was always Lte now it automatically goes to 3g. It is very slow and has become quite frustrating, this has been going on for a while. I have tried "reset network settings" but the problem is still there what do i do?

Difference between iphone and android?

I currently am an android user, but have wanyted an iphone for awhile and might get one for christmas, and i just wanna know, what are the differences? Speed, battery, features etc? Which is better?

Why do people with iPhones receive email text messages?

I have an iPhone and other people I text with iPhones tell why when I text them they get my email instead of my phone number. Why is that is it possible to not to ever send out my email just my number. When I text them with my iPhone.

Can i download apps i bought on iTunes on the play store?

I bought some apps in iTunes on my iPhone and my iPhone broke then I switched to android is there any way I can download the apps without paying for them again on the play store

App that caches YouTube videos for iPhone?

Had to replace my phone when it broke. Used to use mctube but it's no longer available. Does anybody know of an app that is comparable to this that I can cache YouTube videos with?