Hmm, it looks like battery discussions are about as controversial and filled with misinformation as discussions about lightning strikes.
And in my case, the two are related.
I stopped buying expensive batteries a long time ago after figuring out that the cheap walmart Everstart batteries are actually better. About 2.3 years ago, I had a lightning strike and normally I do all mechanical work myself, but I was so overwhelmed with broken stuff both in the boat and the house that I hired a yacht repair mechanic to come do the majority of the insurance claim fixing work on the boat. At the time, my walmart batteries were a couple years old and still performing flawlessly. I was in the habit of using one group 27 deep cycle and one group 24 starting battery since I don't run a fridge or anything super power hungry, i typically just run on the deep cycle and keep the starting battery as a hot spare.
I got home from work one day and the mechanic had swapped both of my batteries out already (without my permission)...saying that he had already authorized the insurance company to pay for them because "sometimes" a lightning strike can cause batteries to fail shortly afterwards. At the time, they were working fine, but I didn't know any better one way or another so I figured if the insurance company was paying for them, then what the heck, I'll just get some new batteries. Well, the mechanic also seemed to be of the opinion of most people in this thread that deep cycle are better on boats than starting batteries so he replaced both the group 24 and group27 with DC batteries. And, he installed two West Marine batteries.
Now I don't usually like to bash companies publicly and I don't know who makes WM batteries, but those things are crap that cost close to twice as much as the Wallymart batteries. I could tell right when they were new that they were taking too many amps when fully charged. I could never get them to suck less than 2 amps right when they were brand new, and by the time they were a couple years old, that climbed to closer to 3. Over this last summer, there were a couple occasions that the battery seemed a bit weak when starting the motor. The starter would turn a bit, stop, then turn some more. I'm thinking, these are crap batteries. And sure enough, about a week ago, I haven't run the motor in a few weeks, so I dip it in the water and try to turn the motor with the supposedly fully charged battery and it won't turn it fast enough to start. So, I switch to the other battery and try it and it does the exact same thing. I could only start the engine by having BOTH batteries selected in parallel.
My cruising season is about to start soon and I don't want to go for long trips with crap batteries so I went to Walmart and bought two brand new ones. I accidentally bought a group 29 with 845 CCA for some reason, but when I looked at my battery box, it looked like a group 29 would fit in there..so, after shoehorning it with a screwdriver, it actually dropped in, so I figure, what the heck, I have an even bigger battery now. And I also went back to one starting battery and one deep cycle because before the lightning strike, the last set I had like that lasted over 5 years and still turned the motor better than the 2 year old WM batteries. This was deja vu as I have had bad experiences with WM batteries many years ago which was what caused me to stop buying them in the first place.
It was so nice to put the 6 amp charger on them and have them draw less than an amp after full charge...like a good battery should.