Lg g3 d851 shutdown problem

Hey everyone i have lg g3 d851 and i am facing a serious problem with it. The problem is when battery is about 40% it starts draining fast and when reaches 30% it shuts off at any time like that battery is pulled out from the device. When i push power button to turn it on it says battery is 0% .. I have tried these means to do get rid off it but nothing worked
Soft reset , hard reset and even after changing battery i am facing same problem..
Can anyone tell what the actually problem is and how it can be resolved.. Please suggest me some reasonable solutions immediately ..
Contact email:mnumangul7@gmail.com
And marslangul7@gmail.com
Thanks i am waiting for your support thanks