I do not know what was changed in lead/acid battery manufacturing over the years. My personal experience has been draining them excessivly does seem to drastically reduce lifespan.. Even once totally drained to me is once too many.

Probably for the last twenty years this has been an issue. Johnson control batteries that used to be the best recommended reasonably priced batteries have become a major disapointment some time back.

They also unlike batteries of old seem not to like sitting unused very much as well. I only wish someone could describe what has been changed?