I think all the 0320 and 0290 engine STCs have moving the battery behind the baggage compartment as an option. I chose not to do that when I installed a 0320 in my AA-1B. Reason for me my STC called out that to move the battery you had to install a Piper 35amp battery box, and of coarse run the heavy gage wire from back there to the relays on the firewall. This makes the battery hard to service and added weight. I chose to just add wight in the tail to manage W&B (I have about 7 lbs back under the vertical fin).
I do understand other STCs moved the battery and retained the 25amp battery, but still the aspect of getting to the battery for maintenance can be an issue for some folks.