Take the batteries back to SAMs, and head to Jefferson Battery. On Jefferson highway right across from the Lowes at the Orleans parish/Jefferson parish line. Their prices are much better than even SAMs, and they provide great service. They can also walk you through the process of selecting the proper batteries.
I just replaced mine, and walked out with 4 6v deep cycle batteries, 225ah each, for I think $350, including new jumper wires. The starting bank is actually a deep cycle set, but has more than enough CCA's to start my 44hp engine.
That is a pretty comparable price to the Deka/East Penn 6 volts under the Duracell name at Sam's.
If you are installing the Echo Charge soon, as I think you are, you have several options for switching.
1/2/both switch works - only problem is that whichever battery bank you select is powering everything.
2 simple on/off switches - start for engine and its ancillaries only and house for everything else. Downside is it doesn't allow for starting from the house bank. This is what I have.
A 1/2/both switch and a simple on/off switch. Use the on/off switch for the engine, use #1 on the 1/2/both switch for the house and wire from # 2 to the output of the on/off switch. This allows you to start from the house when the
1/2/both switch is in the "both" position and the on/off is "off." Diagram below from Bill Trayfors shows it as well as Echo Charge wiring. This gives you the most flexibility.
The install of both the Echo Charge and the Victron monitor are very easy.
I haven't heard anything bad about the Iota chargers - I installed a DLS-55 just last week.