[Q] Stuck! Phone does't turn on and does not charge

Hello guys I have been struggling for the past week, my LG G2 phone has been rooted, I flash a custom recovery TWRP then I lunched to my stock rom I then tried to update my firmware to 4.4.2 kitkat the update was downloaded successfully, then it told me to reboot, so I did phone switched off then I was stuck on a boot loop but this time it was a boot loop with a error message on the left top corner. and then it would take be to a dim back screen. I searched the entire week to find a method to get me through the start screen and I found this -> NO Recovery mode, No download mode, after OTA on rooted LG G2 http://xdaforums.com/showthread.php?t=2582142 I done exactly what it was showing, then my phone switched off and now it won't power up. Then I tried turning it on NOTHING phone does't show the LED charging lights, does't respond to the usb being plugged in can't do ANYTHING I am guessing the battery has died so now I don't know what to do, either contact LG or should I try getting a battery that is fully charged or even use a factory cable any ideas guys ?