Anyone who is considering removing the battery tray in a first-generation Acura TSX should take note of one thing–this is the most sturdy battery tray I’ve ever seen Honda put into a vehicle!
It turns out that not only is the tray held in by two bolts from the top, there are two underneath the tray, installed horizontally, that screw in towards the direction of the adjacent fender. The best way to find these is to use a skinny LED light and a mirror–otherwise, it is difficult to feel your way around to find them. Also, the bolt closer to the front of the vehicle is tucked slightly behind the air duct, which you cannot remove until the battery tray is removed. So…yeah, it’s a bit tricky to get to.
Also, a very important tip about removing those two lower bolts–don’t remove them! I only found out during reassembly that the battery tray bracket has slots, not holes, so you only need to loosen those bolts a few turns to remove the tray, pulling it straight up once the bolts are loosened. However, you might remove them anyway, once you slide the tray out, in order to apply some anti-seize. Bolts like these have a tendency to corrode and seize up. Make it easier for yourself, or the next person, to loosen these if needed.