Not exactly an apples to apples comparison, but I bought my boat back in October of 2021, of which in the fall of 2023 I got a low voltage warning as well when taking my boat out of the water for the season. So, I figured it was time to replace the batteries, as I bought the boat with batteries of an unknown age, where they didn't have date codes on the stickers or anything. The applicable portion here would be that I called up my local Grady White dealership and asked them about which batteries I should replace the current ones with, of which they said to buy new batteries of the same size, style and material as what I currently have. My boat came with two Group 24 starting/cranking wet cell batteries, and that's what I replaced them with... two Interstate brand 24M-XHD batteries.
I brought up the AGM battery question to them, if it was worth spending more money and buying that style of batteries instead. Of which the tech mentioned that he wasn't a huge fan of the AGM batteries. He said that they seem to be rather temperamental, and might get you 2-3 seasons at the most of battery life. But that they are very sensitive to vibration, stress, bouncing around on boats, etc, and he said they've had several come back that they had to replace because they failed prematurely. Long story short, he said I could spend double the money and get roughly about half the working battery life out of an AGM compared to wet cell batteries. But he instead recommended that I spend half the money, get a good wet cell battery that should last for 5-7 seasons instead. At the end of the day, your boat, and especially I imagine the batteries being only a year old are still very likely under warranty. If your local Grady White dealer is recommending you swap the "old ones" out for new wet cell batteries, I'd listen to what they have to say. Good luck!
