Lithium batteries have become commercially important power sources because they can supply significantly more energy for a given volume or weight of cell in comparison with conventional cells, such as alkaline zinc or nickel-cadmium. The reason is that lithium is the lightest metal and has one of the highest electrode potentials. One kilogram of lithium can supply 3860 ampere-hours of electricity in comparison with 820 Ah for zinc or 260 Ah for lead. However, because lithium is such an active metal, it reacts with water. Therefore, lithium battery electrolytes must be based on nonaqueous solvents or polymers, manufacture must be carried out in specially constructed dry rooms, and safety precautions are necessary both for use and for disposal of lithium cells.