No problem here and I own 32 of them in various applications. Proper grounding, good charging systems, routine service and battery disconnect switches make a world of difference or disengage the DC battery fuse on generators when not in use. I keep them charged. The problem is the buildup of sulfates on the plates. On our 5-tonners, I use 24-volt, solar powered, desulfators that treat the four batteries. This is NOT a battery charger. The unit routinely fires an electrical pulse into the four batteries and prevents buildup on the plates. Never purchase a reconditioned 6TL from Interstate or anywhere else unless it is an emergency and you need it to get home because that is about all you can expect from it.
Yes, there are cheaper alternatives and I have tried them all but for my use and money, I cannot beat a good 6TL