Those are just balsa wood blocks carved to match the convex shape of the starter body with some crude paint on them. The block is RTV cemented to the top of the battery case and directly to the starter case with the switch off to the right side a bit in the normal location for starting the airplane with your right hand which everyone does.

It was just a very neat way of doing the addition very easy and quickly no matter what starter you have also thats another reason that this particular Harbour Frieght battery is a natural since it has a nice case with a flat top that lends itself to this. However they have another 12v drill battery that looks the same except it has a long protrusion on top that fits one of thier tools. This one would be more difficult to use.

As far as durability is concern I have dropped one of mine off the starting bench twice to the hard ground and it did not separate. If you use the RTV though you must let it dry untouched 24/30 hours.

John

Here are earlier pics of the same two when I was using a fancy rubber banded and bolted carrier and this is just not neccessary: