Why is my iphone 4s constantly dying?

I've had a iPhone for about a year now. My first one had some internal hardware problems so i took it to the apple store. They couldn't fix it so they gave me a refurbished one. I've had the refurbished one for about 6 or 7 months.about a month ago i was using my phone how i normally use it (listening to music, twitter, instagram, texting, playing candy crush) & when it got down to 20% it died. That was strange because i can usually get another 30 minutes to a hour out of it at 20%. I waited about 5 minutes and tired to cut it back on and it came on but it was at 18%. I made it home when it reached 3% and instantly put it on the charger. This same occurrence happen a couple more times after that but i didn't think anything of it.today the same thing happened but the first time it died at 46%, then at 32%, again at 26%, and at 20% which at that time i just left it off. Now i'm starting to think since this is a refurbished phone this was the initial problem with it before it was fixed.could someone please help so i can avoid waiting in a overly crowded apple store for assistance

IPhones are very bad with batteries through time. Here is a few ways to save the battery, in a big impact.

- Brightness
- 3G/4G turned off when not needed
- Double tap the circle and exit all your apps
- Lock your phone when not using

Also if your iPhone is in the heat or in the sun, it will drain dramatically. I love the phones but I can't deal with the care you need to give them.