Help Battery Issues

[iSyn]

My S3 (T999) has been having battery issues and it has only gotten worse. I only get an hour or 2 of screen time. I wanted to ask you guys what you think might be the issue before I do anything. It was really bad before I rooted, maybe even worse. Now I'm running CM 10.2. It even shuts off randomly when it gets to the 10-20%. I would love to know what you guys think the problem is. Whether it be a problem with the phone's hardware, software, or just the battery alone is defective.

Here are some screen shots.
This is after it randomly shut off and I turned it back on.

Screen Time:

Apps:

This was after I let it stay dead after it randomly shut down again. Percentage goes back up to 20% randomly.

 

[Netcat]

I had a Galaxy S2 that developed a similar problem with the battery draining fast. The USP port was damaged and the phone thought it was plugged in most of the time, even when It was not. This caused my battery do drain very fast when it was unplugged.

I also had a screen like your third picture that showed something like "20% - Not Charging" when it was unplugged. In my case I think the Not charging statement was because of the damaged USB port. It thought it was plugged in when it wasn't, that's why it showed ...Not Charging. It should show either "Discharging" when not plugged in, or "Charging" when it is plugged in, but not "Not charging".

 

[tube517]

Might be USB port like Netcat mentioned or it might be the battery. Do you have a spare battery to try and/or a spare USB charger to try?

 

[Muilisx]

My battery life sucked too at first, but after 3 full charges and discharges, and the phone starting to learn me. I'm getting GREAT battery life.

People don't realize that even though the new batteries phones have these days aren't like old remote control car batteries to where if you didn't full charge and discharge it, the battery wont ever charge fully again. Even though that WILL NEVER happen with the new technology in batteries. It's still wise to fully charge a brand new phone before you use it, and fully discharge it to where it turns off on its own BEFORE recharging it. I did 3 full cycles of that and I have no issues with holding a long long charge for the whole day now.