What's up O&B!?
First up, equipping your boat with a Blue Sea Systems ACR (or Automatic Charging Relay) is one of the smartest things you can do for your electrical system to keep you trouble-free on the water.
An ACR system monitors voltage across all battery banks and delivers a charge where it's needed most. This not only keeps your electrical system at it's optimal voltage but also extends battery life by preventing overcharging -essentially cooking- your battery banks.
My ACR system was installed by HarborMarine.net and I couldn't be happier!
My advice on the actual batteries would be to install AGM or Absorbed Glass Mat batteries in Group 31 size. These larger, more robust batteries are essentially dual purpose starting/charging and fit the bill for the type of boating battery we need 'round heah!