90% of all lead acid batteries lose voltage due to plate sulfation. 8% is due to plate deterioration and 2% is due to interior shorting out GUARANTY This product comes with a product replacement warranty. We will replace Tenacious Battery Revitalization System™ if your new battery fails to perform for an additional 18 months beyond the battery manufacture's warranty, if new, or 18 months after injecting our fluid in your existing batteries. Exception to the warranty: Batteries with interior physical damage will void this guaranty. A simple testing of the density of each cell, a load tester and a voltmeter reading will determine this. On large 24volt plus batteries with multiple cells where one, two, or three cells have physical damage we will treat the replacement cells with our Tenacious Battery Revitalization System ™ for free. Standard battery maintenance is required, i.e. water levels are at proper levels and the batteries are charged and cleaned as necessary.