final thought, you should add a fuse in-line with the positive side of the battery so that a short in the wiring harness won't cause the battery/harness to melt. Only caution is that when you plug the 1/8" mini plugs into the ps2/ad20, the plugs will short while being plugged in (which, if live/hot will cause the fuse to blow) -- so, put a connector downstream of the fuse so you can a) plug in the harness to the ps2/ad20 and then b) plug the harness into the battery -- this will also be useful so you can use harness with each of the 2 batteries you bought.
darrin