The 3rd gen Tundra's secure the battery to the vehicle by clamping the bottom of the battery to the vehicle. There is a thin tab extending up that gives you something hold onto while tightening the lower battery clamp bolt (image 1).
Image 1: Battery tab before bending
You simply need to bent it back so its out of the way. Its not difficult and can be done with just your thumb. (image 2).
Image 2: Battery tab after bending
This creates room for the mount in front of the battery and doesn't compromise any structural integrity of the factory battery mount or PowerTray.