need advice on a battery

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Man battery maintainers are battery's best friend!
Icechest radio AGM battery installed in 2008 stays on maintainer still plays radio for more than 24 hrs with a small amp!

My mud boat battery is a NOV.07 off brand no maintenance that is still cranking today, no ****t! On a maintainer

My bay boat came with cheap wet cell batts, that lasted 2 years I did not keep them on the maintainer and the winter temps pulled them down and weakened them soo they got tossed, I then replace with AGM's in Jan of 2010, and they are still cranking and trolling me along, and I've yet to have them go dead on me during a trip. Also on a maintainer

And last but not least, I get a kick out of this my 2005 dodge ram 2500 diesel had the same batts from June of 05 until aug of 2011 110,000k miles later, I replaced with dodge batts and there cranking me every day still!

I strongly believe the maintainers are a huge help, and I really lucked out with the truck batts, but Im 3yrs into the new ones and they are trying to spin the starting gear off the bendix. Is it all just luck?