I have a starting battery built in to a small box right under the windlass. It is wired into the charger with the genny battery. I really do not anchor out a lot so it is a comfort to me to know there is a fresh battery sitting isolated at the bow of the boat that I can swap out with the other batteries in the event of a failure.
The two smallest batteries on the boat are the windlass battery and the genny battery. Having an 8D for those two machines seems like overkill. Plus, although an 8D might make a good emergency battery if you have long jumper cables I would certainly hate to have to "lug" one of those monsters very far. In fact, that is why I got rid of mine.
pete