^^ Correct, this was the external battery. It lasts me close to 6 hours because I have automotive relays on the after-market remote that shuts down the motors when I pick up the tennis balls and make sure I don't waste the power. This is originally a Silent Partner Lite machine. There are a couple vertical tabs at the edge that need to be cut in half as seen in the picture and the opposite side has two vertical tabs that need to be removed. I put padding in the well of the stock battery footprint that sort of cushions the big battery.
Drill two holes on each end for an aluminum bar, drill holes, screw and nut, leave loose while looping the straps around, pull tight. Then tighten the aluminum bars down flat to the plastic base. It's pretty solid. I'm going to finish this today and put in a new mode so I can push a button on the remote to eject just one ball and stop.
I have a 4 button remote. Motors on/off, Ball Feed on/off, Oscillate on/off, One-shot ball feed.