Default G2 Screen goes black at around 50% battery level.

History:

Phone was warrantied after it locked up during KK update. LG Canada replaced the board.

Current:

Had it for a day, loaded everything back on (apps, photos, contacts etc..) and in the middle of uploading my backed-up videos the screen goes black. I can hear the tap/swipe noises when I touch the screen, but nothing brings back the screen. I try turning off/restart, holding the power button for 20+ secs, and confirming that it's not just in lockscreen. When turned back on, I can hear the LG splashscreen but the screen is still black.

Later that evening, I planned to set the phone to charge for the night and see if it was a battery issue. With the phone completely shut down, I plugged in the micro-USB quick charge and to my amazement the charging battery graphic appeared. I powered the phone up and everything was fine.

It has happened a few times, and all around when the battery reaches the half-charge level.

Anyone else experience this? Any way I can troubleshoot?

Should I just warranty the phone again - or get it replaced?

Thanks.