Many things effect batteries; the greatest of which is owner ignorance, bringing up the next to greatest which is lack of maintenance or proper care.
With batteries, rather than reading our comments, which are mostly opinions, go to Google, seek out one of the major battery manufactures website, (Deka is the largest manufacturer in the world- look up that one)and read the facts.
There you will find that starting with two new battries that receive a proper initial charge is necessary. Don't expect the selling place to give them a proper initial charge. Then, DEPENDING ON WHAT TYPE BATTERIES YOU HAVE PURCHASED, you must be aware, through the use of a digital volt meter, to what level you are 'using down' your batteries prior to recharge. Water levels are crucial. Sulfation control is extremely important, which can be controlled during storage, through the use of a Battery Maintainer- NOT A REGULAR CHARGER OR TRICKLE CHARGER!
If your equipment, that is powered by the battery is faulty, then it's not the battery's fault. Also, if you discharge them too deeply, or don't keep them charged PROPERLY, especially during storage, it's not the battery's fault.
With you having so many problems, it is possible you have a piece of bad equipment, your cables may be faulty, your charger may be charging too high (boil out the water) or too low and letting the batteries sulfate. Many parts and pieces to the puzzle to make it work properly. I might suggest, however, that with that many batteries going bad, it probably is not the battery manufacturer's fault.
2000 390 Landyacht XL
1989 29' Excella
WBCCI #6673 jerry Hodge
Have no intention of arriving at the grave safely, but rather to skid in sideways, chocolate in one hand,throttle in the other, totally worn out and screaming
"WOO HOO, WHAT A RIDE!"