Battery arrived today. I ordered the Odyssey battery. This is what the holder was made for. Some others are looking at new technology, but Odyssey has a good reputation of working without issues. Its a heavy little battery. I could barely lift it into position with one hand.
It fit in. I hooked it up. I simulate the airplane environment with my power supply by hooking it up and running it at 14.2 Volts. The batter gets a little charge from this and I run the airplane systems just fine for testing.