What Are the Benefits of Switching to AGM Batteries?


My boat came with two starting batteries and I want to switch to AGM, what should I look out for? I have two 24M-800(CCA) 1000 CA starting batteries that came with the boat when I purchased it new. I don't leave them in the boat over winter from early November to early March. They are stored on my work shop wood bench in a heated garage over winter and are charged approximately every six weeks. They will not hold a charge for any period of time. I am thinking of changing them out with AGM batteries. A #27 series and a #31 series batteries. Can AGM batteries be used for both starting and house applications? All the research I have done on AGM's state they are good for both applications. Also , why would ether the manufacturer or the dealer put two starting batteries in the boat? Thanks in advance I look forward to your reply. - Lyn


Hi Lyn,

AGM batteries can be used for both starting and deep cycle applications.   As to “why would either the manufacturer or the dealer put two starting batteries in the boat”.  Probably one of two reasons: cost savings, starting flooded lead acid batteries are less expensive then flooded deep-cycle or ignorance, many decision makers don’t appreciate the difference between starter and deep-cycle batteries

Hello again Jeff,

Is there anything I have to be aware of if I switch the batteries in my boat to AGM.  The motor is a Yamaha F300XCA offshore motor. I’m told that dual batteries are an option to this motor but was set up as dual. What I understand thru the web sites I have visited that the charging amperage on the alternator may or may not be a problem.  What would you recommend for AGM battery size in this boat.  Thanks in advance again…I read all your articles in PY Magazine and look forward to them on a monthly basis. Your articles are very informative.

Thank you Lyn,

If going to AGM you’ll need an AGM compatible battery charger. Having a AGM charger removes the absolute need to get a alternator that charges to an AGM profile.  In terms of sizing the battery, I’d follow the engine recommendations vis-à-vis CCA and get an AGM battery that matches or exceeds the CCA rating of the engine.