I finally need to replace the last of the original batteries on our trailer. I wanted to get an Optima D34M blue top battery from Costco, but see that it's only rated for 55 Amp-hours (20-hr rate). In contrast, the batteries I had originally were each rated for 115 Ah and Costco's cheap size 24 marine deep cycle battery is rated for 85 Ah.

Can someone explain this apparent discrepancy to me? Is it still worth getting the Optima battery?

Thanks!

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Tim, wife Beverly, & two boys who love RV'ing
2005 Sunnybrook 30FKS Dual Cam HP
2002 Suburban K2500 8.1L 4.10 Prodigy