The length of the warranty is not indicative of the strength of the battery. Some battery cables will have a smaller wire, soldered to the terminal, which is used to either operate a smaller device or to provide an additional ground. When the smaller cable burns it indicates a high resistance in the heavy cable. Even maintenance free batteries need periodic inspection and cleaning to insure they stay in good working order. Inspect the battery to see that it is clean and that it is held securely in its carrier.
Some corrosion naturally collects around the battery.
Electrolyte condensation contains corrosive sulfuric acid, which eats away the metal of battery terminals, cable ends and battery holddown parts. Rinse with water.