Thanks for the comments. All sounds logical. BTW, I have two Group 27 batteries on a [Off - 1 - Both - 2] switch.
I was looking at the Costco Group 27 Marine battery ($83; was $69 in Sept 2010!). It is labeled as Starting/Deep Cycle, 750 MCA, 115 Amp Hours, reserve capacity 160.
So I really don’t know if it is a true Deep Cycle, but it sounds like a dual purpose. I’ll check next time to see if there are more details or manufacture identified.
Charlie Lincoln • Cathlamet, WA • Islander 28