Battery problem

[AC Question]

So the battery will charge to max 81%, even after overnight charge, when it reaches ~20% it will start to free fall, no matter what the use, it can only be charged when the phone is off, when it's on it actually acceleratingly starts to go down.
Then it's definitely empty, you can't turn the phone on. I tried calibrating and switching charger and cable but it doesn't change.
I think I've got a faulty battery but can't be sure if it's not software problem and I'd like some second opinions as I'm new to android.

I have a 2800mAh at 3.7V, 5" screen at min. brightness,3g off,no mobile internet and apps,android 4.2

https://www.dropbox.com/s/751bjyft9klvnh9/Screenshot_2014-06-30-10-02-28.png , rising and flat is charging while off
https://www.dropbox.com/s/ev4v14ttm94r74t/Screenshot_2014-06-30-10-02-35.png , voltage
https://www.dropbox.com/s/6xdbsmy8uxkb8on/Screenshot_2014-06-30-10-01-28.png ,android's usage statistics

Thank you for any help

 

[Golfdriver97]

Welcome to the forums.
What device is it? How old? Is the battery removable?

 

[David X]

dg500c, it's a chinese brand but the company is reputable. I got it 4 days ago. Yes it's removable

 

[Golfdriver97]

dg500c, it's a chinese brand but the company is reputable. I got it 4 days ago. Yes it's removable

Try taking the battery out and see if it bulged. This is easily done by placing it on a table without a tablecloth and trying to spin it. If it does the battery is defective. Even if it doesn't spin, the battery may still be defective.

 

[David X]

It's not bulged. So you think the problem definitely is in the battery? I could return it but how much time can I expect to get in one charge for phones in 4.5 - 5 inch range?

 

[Golfdriver97]

It's not bulged. So you think the problem definitely is in the battery?

Most likely, but it could also be the physical charging port, too.

I could return it but how much time can I expect to get in one charge for phones in 4.5 - 5 inch range?

Kind of a loaded question. Too many variables, like screen brightness, timeout, cell signal strength, app syncing, etc, can all affect that.