Both 6v and 12v batteries get old very slowly if they are kept charged and stored off the ground.
Corrosion can be eliminated on both 6v and 12v systems: clean contact areas and use an anti-oxidant highly-conductive "grease" on terminals and ground/hot cable connections (di-electric grease is not conductive).
NAPA - 7652569 (small "jar")
NAPA - 7652568 (small tube)
NAPA - 728283 felt corrosion protector rings are an inexpensive addition
