Heavy discharges, temperature, vibrations, rapid charging, and overcharging all increase the process of "aging" of a car battery. The reduction of water for normal recharge charges due to lack of maintenance, evaporation from excessive under-hood temperature, or overcharging contributes to almost half of all early automobile battery failures.  Sudden failures are also caused by positive grid corrosion and undercharging, which causes oxidative stress. Positive grid corrosion causes an open connection in deep cycle batteries that are typically well handled and charged. Another reason is the erosion of active materials.