Looking for a solution:

In the past, I have always relocated the battery to the right rear of such vehicles as the Ford Mustang, Chevrolet Camaro, VW GTI , and Mazda RX-7; and so it was that I had all planned out for a relocation in the STI.

This was proving to be problematic, however, as the location one would likely move the battery to is occupied by a water container.
The container is used to supply the Intercooler Sprayer System on the STi, and it really wasn't going anywhere.

So, I thought of 2 other locations.  How about behind the passenger seat or behind the rear seat in the trunk? Placement in the trunk though, would require an additional On/Off Switch for Track use.  One quickly determines that these locations are not ideal as both areas would be difficult to orchestrate. Plus, a Battery Box would be needed, along with new Battery cables and connections.