Both batteries are Group 24 wet cell from West Marine. The starting is brand new, the old one was dead, and is 1000 MCA. The deep cycle is about 4 years old with 75ah and has 650 MCA. The deep cycle tested out as 100% health.
Without the engine running I have moved the selector between 1, 2 and both and nothing dimmed or switched off so I must have the right type. I will verify this again but it looks like I can manually control which one is charged for right now.
I do like the idea of the Duo Charge or similar charge regulator and have added this to my project list. I thought with just a simple 2 batter system using Both to charge was adequate, it worked for like 5 years. I didn't realize even that way one battery would be charged more than the other.
You will regret the things you did not do, more than the things you did.
Get out there!
Saco Bay, Maine
2001 Beneteau Oceanis 361