My experience has been they last a long time. Last one I killed lasted 13 years. I have also learned I don't car for them in a race car that requires charging. The reserve capacity isn't great enough. They don't regain a lot of capacity unless slow charged. Therefore if you run a small alternator and big power draw they didn't like to go more than a few days of racing with out a slow charge. That made 3 day and some 2 day events tough unless you could plug in the charger or run the generator over night.
Doug