Is there any way I can fix my phone from dying so fast (iPhone 4s)?

My phone is an iPhone 4s which I have had for over a year. My two year contract ends in like 4 months in august and that's when I can upgrade.
My phone dies when it still has up to 40% and says it needs to be charged then all I have to do is plug it in and it will turn on and be at 40% once again. This happens to my phone at any percentage that is below 40 and 40 is the highest percentage it's ever died at.
My phone also dies fast. I was at a venue a couple days ago and I had to turn off my phone while I was there so I couldn't really take any pictures of the bands playing which sucked. It was 5 bands and I would turn on my phone in between sets and text my mom and then turn it back off. But nonetheless my phone still died that night and I had to text my mom from my friends phone to pick me up.
I can't get a new phone for 4 months is there any way I can fix my phone?

I'm going to go ahead and say no. No way to make it any better.

For your next phone. Try to keep your phone in between 25% and 80% thats sort of the sweet spot for newer phones. Turning them off or running them dead is really not good for it. On the other hand you don't want to leave it plugged in on 100% all day either. Its not bad to run it from 100% to dead once a month or so. That should help your next phone from having the same problem.