The Apple Li-ion Internal Battery For iPhone 6 is a branded and original replacement battery that works perfectly with the 6 model. It has enough power to charge the phone once over due to it 1810mAh capacity, which is the same as the original battery that comes with the iPhone 6. It is a zero cycle battery and has never been used.
The battery can be replaced easily, but does not come with the required tools to do so. You will either have to buy the tool set separately or take it to an Apple care center to get it changed properly.