I try to avoid spade bits- as abusive to the drill as they are to the operator. Ever considered a small auger bit? They are long enough you won't need an extension and since they are 1 piece.. nothing to loosen or fall off inside a wall. Just make sure your batteries are well charged. I love my 1/4 auger for doing little stuff- that and a cordless drill is like a mini-holehawg.
