I bought a JD4100 in 1998 and the battery was still going strong when I sold it after 10 years and 1000 hours use. Bought my 2520 in 2008 and battery is still good after 400 hours. I use my machine at least once a week year around and if I don't use it for a week in the winter a put a trickle charger on the battery. I think you can get more life if you keep them charged well.