iPhone 6 plus not charging

I've made my iPhone 6 plus due to a technical problem. I received the new one short a time ago and I'm syncing the brand new iPhone 6 plus right now, via usb cable which came from previous iPhone 6 plus box. It doesn't have a problem at being recognized by my computer & syncing. There's a charging icon on both my iPhone & computer. But iPhone doesn't actually charge! Power percantage is always dropping down. What I should do? I need an answer ASAP please, thanks