My last 6v battery was from Central Tractor Supply and lasted for 11 years. I always use a Battery Tender and a battery cut-out switch when it's in storage for more than a week or so and check the electrolyte level often. If the level is low, I always add distilled water - never tap water.
I also had a 14-year old 12v battery in my wife's '71 Olds Cutlass, which was also maintained the same way.
And yes, I'm a compulsive record keeper. I keep a record of evrything I bought for all of my cars, when & where it was purchased and the cost. :rolleyes:
-Bob