When I bought my boat I learned that the installed automatic charging relay was broken so both battery banks were always combined. The banks are a house battery bank (4 Interstate Deep Cycle Extreme GC2-XHD-UTL golf cart batteries for a total of 464 Ah across all batteries) and an engine starting / bowthruster battery (Interstate Deep Cycle SRM-29 with 675 CCA/845CA). With both banks combined by default, the engine always started instantly. After disconnecting the ACR, the engine starting battery would no longer start the engine. The engine would crank slowly but would not start. The engine is a Perkins Sable M300Ti. I assumed the battery must have been worn out so I bought a generic Autozone marine deep cycle battery with 675 CCA/840CA to test that idea out. I charged the new battery before installing but still only got the engine to crank slowly. Since the engine starts easily when both battery banks are combined, it seems the straightforward solution would be to get a more powerful starting battery. However, based on the guidelines in the table below, I think this battery should be able to start the engine. Am I correct about that? If so, what other issues might I be having?