Why is my S3 battery complete garbage?

[AC Question]

bought a used s3 few days ago and battery life is complete ****

I bought it used, realizing that he was selling it for a cheap price because of the really bad battery life. My friend had a s3 before so she gave me her battery for me to use as a spare, because the original die really quickly. Like it decreases a percentage by the minute. I can't last longer than 2 hours. I also am using it unlocked so no call and text, just*
minimal use of kik, snapchat, instagram, and rare usage of internet and youtube brightness is always at the lowest, not even at auto, no live wallpapers, barely any music played, and i keep it off during classes.
Even with using the spare battery i have to charge it just in case it dies at school. My other friend who has a s3 at the moment, i tried her battery which has been used for 6 months new, it made no difference i still was dying by the minute. I'm really hoping that its not the phone thats the problem so please don't tell me it is. Is there a cheap solution for my problem? Should i get it fixed by someone or should i buy a new battery and where or should i cry about how bad my luck is? Please help.
Just by typing this up i lost 15%.

 

[belodion]

Welcome to Android Central.

Before going any further, what do your battery stats reveal to be the main users of charge, after the battery has discharged to say 50%?

Also, what sort of signal quality do you have? I'm not clear from your description whether you're using mobile data and/or wifi, but either way, a weak signal will eat battery.

Also, are all your basic settings, such as syncing and location reporting, set with battery saving in mind?

If we can help you get this fixed, we will.

Posted via the Android Central App

 

[ropluto]

I think the screenshots will show how my stats are for my phone.

i don't use any phone network so its unlocked. I only use it from WiFi from school, home, restaurants etc. But their wifi signal i think isn't that bad especially at home, my laptop works fine with the home wifi.

no the only setting that is on daily is wifi and power saving. I would assume if i keep any other settings on that that will as well eat the battery.