IPhone 5 problems, battery/volume buttons

I've had the iPhone 5 since it came out, my battery used to shut off at 40% every time I was taking pictures or playing music, but after a few months it went down to 20% where it shut offs, it's been over a year and a half, and I can't take it anymore, it's driving me nuts, what can I do? Also, my volume buttons broke a long time ago, they were basically stuck together, so if you pressed the volume up button, it stayed pressing up until you could balance it, recently they started working again although I hardly use them as I'm afraid they'll stiff up again. How can I get the volume buttons fixed so I'm not worried about them breaking again and fix my iPhone from dying at 20%? I don't want to spend 100$'s at Apple's store getting this fixed, what are the estimated charges?

But don't worry hope these tips help you fix your iPhone…

THIS 1ST STEP WON't DELETE ANYTHING ITS BASICALLY LIKE A SOFTWARE TYPE A FIX…

. First Hold the power and home button, notice how the screen will go blank don't worry KEEP HOLDING BOTH BUTTONS, then once you see the Apple logo appear then move fingers away from the buttons let it boot up… See if there's any success this step includes the volume issue…
try the volume buttons…

if this doesn't work rest as a new iPhone by going to iTunes with your iPhone plugged in to the pc, then after its as new like when you got it without music or content including apps, etc… See if the problem is solved?

if all else fails then there's something wrong with the flex cable which works the power, volume buttons etc…

In other terms for the volume button error you can:

Go to Settings> General>Accessibility> AssistiveTouch then turn on

you will notice a small circle thingy on the screen tap that, you will see these options tap> Device> then you will see the volume up and down and other things eg: Lock screen, screen rotation etc…

you can control your volume from that thingy too…

Hope this Helps?

Enjoy your Day.