There is no simple answer to this. I’ll start with the easy part – for *non life-cycle cost* issues, flooded loses big time. We used to have flooded batteries and during Hurricane Charlie one of them broke open. The smell was an extra special treat and then some and that is before you add salt water to the mix, which gives you some nice chlorine. Flooded batteries have acid that can spill, can produce corrosive gases, will produce hydrogen that can explode, and can be all around dangerous and nasty. Obviously people do use flooded batteries on boats, although AFAIK you cannot on a racing boat anymore, but they take some care to secure properly. In our boats the batteries can be right under where someone sleeps, so this is really important. On to life cycle costs. I am leaving lithium batteries out of this whole discussion, that is a big $$$ commitment and is an ever changing field right now. Long story short – Golf cart batteries win and win big on life cycle costs. 2 6 volt 220 AH golf cars are probably around $200 total for both and are designed to be cycled and abused. You will get the most AH for the $$ no doubt and many a cruiser uses them. If you are not racing and have a place to safely secure them, I would give them strong consideration. The various car battery type marine batteries in my experience don’t last all that long unless they are a true deep cycle. Trojan makes some and I am not sure who else is a good brand today for that. It has been a long time since I bought wet batteries.
Moving on to solid/gelled electrolyte batteries, they have several advantages and some big disadvantages too. First off, there is more than one kind. Gel cells are NOT AGMs and AGMs are not gel cells! I have gel cells on my boat. They cost more than AGMs and have about twice the cycle life of the commonly sold AGM batteries. They are hard to find, expensive, and have specific charging requirements. Overcharging kills them quickly, you need battery chargers designed for them and an alternator regulator that can be set for them. They have the advantage of long life if treated well, have no liquid to leak, will not off-gas unless badly abused, and work mounted at any angle. One very nice thing about gels is they have a very low self-discharge rate. Wet cells usually lose around 10% a month and gels are more like 1%. Back before I had shore power or solar I had no issue winterizing in December and starting the engine in March even after using the occasional light over the winter with no charging. AGMs are another solid/gelled electrolyte type of battery and are far easier to find than gels. They usually have about half the cycle life of gels and also have specific charging requirements that are NOT THE SAME as gel batteries. They are far more tolerant of higher charging voltages. What kills them is not being topped off to 100%. If you have no shore power and no solar, they will have a short life unless you motor everyplace you go. AGMs can be found relatively cheap if you know where to look. East-Penn Deka makes all the West Marine batteries and they also do (or did, haven’t checked recently) make a private label Group 31 AGM for Sam’s Club that they were selling for less than 50% of the West Marine price for the exact same thing. I think Sam’s labeled it an “Energizer”. Joe Coquina
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