[Sprint Samsung Galaxy S III] bryantobing:
Let me start with some details about the phone:

- It's a Sprint Samsung Galay S3, SPH-L710

- It was rooted and Cyanogenmod was installed successfully, no problems

- Phone was given to my aunt, and she used it for a while

Here's the problem:

A little while ago, she told me the phone turned off and wouldn't turn off again. I told her to charge the phone and see if that helped. She charged the phone and waited for the battery animation to show up full, and then turn on the phone. It booted past the Galaxy S3 logo, past the animated purple Samsung logo, got halfway through the Sprint 4G LTE boot animation with the music and then boom. Shut off. And then back to the battery charging screen but displayed the battery as if it was only 15% remaining. What?? Wasn't it full a minute ago???

Here's what I did to fix it:

Okay so I thought, it's a battery problem. I purchased a second battery from eBay (not OEM) and the same issue occured. Same exact thing happened. I looked up the issue online and it appeared to be a soft brick. I forgot exactly what I did but I downloaded a recovery file and flashed it via ODIN and it turned on. Phew.

I gave the phone back to my aunt and a week later, the same thing happened. Phone dead. Won't start. Won't get past the Sprint boot animation. So I thought to myself, hmm ok. I'll just reflash and do what I did before. But I mean, how often do I have to keep doing this? And she loses data every time I have to flash the phone.

And so I did. I put it into download mode, opened ODIN, browsed for the md5 file (I forgot what file it was, I'm mad at myself for that now) and flashed the phone. It flashed successfully but this time, the phone wouldn't turn on. It kept vibrating as if it's about to turn on but then dies immediately. I left the phone on my desk for a while and all I could hear was *bzzt* [pause] *bzzt* [pause] *bzzt* and I'm thinking, okay. Time to get an OEM battery.

I finally found an original Samsung battery from an authorized Samsung dealer, I was pretty surprised he still had the battery in stock and bought it from him and ran home. Still the same thing. Kept buzzing but won't turn on. And if I do turn it on, it won't get past the Sprint boot animation.

So I looked and looked and looked and looked online and found this: http://xdaforums.com/showthread.php?t=2755793

Long story short, I followed the instructions, flashed successfully with no errors, and now I can boot past the Galaxy logo, boot past the Samsung logo, and finally past the Sprint boot animation until I landed on the Samsung screen. Just a black screen with Samsung that seemed to have a glowing purple around it. I was getting excited. After about 10 seconds, it went to the main welcome screen (the Google setup thing) with the next button and the language selector in the bottom. I was on that screen for about 2 seconds AND THE PHONE TURNED OFF. Back to the battery screen.

What am I doing wrong? Is there something wrong with the phone? Battery? Am I flashing the wrong software? If so, can someone please direct me to the right place?

P.S. If you're thinking, "dude just get her a new phone" she does have a new one now. It's a Galaxy S7 but I really really want to know what's wrong with this phone and it's been annoying me lol