Could it be the current in your dwelling is a bit funky? I't just seem like there's a cause for this to be happening that has been dismissed or overlooked.
This is rare to happen once,but with every phone, there is a cause. Trade in your charger and USB cord. If that doesn't solve the problem it could be the current in your dwelling or you. I've heard of people that had a electrical current that keep them from wearing wristwatches(they would quit).