the normal capacity of the cell is insufficient, short increased rate charges can be given provided that the temperature of the electrolyte does not exceed 115˚ F / 46˚ C. These short charges are very efficient and cause no injury. Rates up to three times normal charge rate (defined as C, the current equal to the nominal capacity of the battery divided by 1 hour) can be employed for periods of 30 minutes. Fully charging a NiFe cell consists of seven hours at the normal cell rate. In service the amount of charge given is governed by the extent of the previous discharge. For example, a battery discharged one-half, allows a 3.5 hour normal rate charge. Overcharging wastes current and causes rapid evaporation of the water in the electrolyte. For tapering rates of charge, an average of 1.67 volts should be maintained across the cell terminals throughout the charge. The current value at the start of the charge varies according to the electrical resistance. Absent resistance, the starting rate will be about twice normal and the finishing rate about 40% of normal. Discharge Under discharge the positive plates are reduced ("deoxidized"); the oxygen, with its natural affinity for iron, goes to the negative plates, oxidizing them. It is permissible to discharge continuously at any rate up to 25% above normal, and for short periods at up to six times normal. When the discharge rate exceeds this value, abnormal voltage drops will occur. Electrolyte The electrolyte does not enter into chemical combination to perform the functions of the cell, acting as a conveyor. Its specific gravity is unaffected during charge and discharge other than through evaporation and changes in temperature. Considerable variation in specific gravity is permissible, having influence only on battery efficiency. Environmental impact Nickel–iron batteries do not have the lead or cadmium of the lead–acid and nickel–cadmium batteries, which require treatment as hazardous materials. Nickel-iron batteries do not cause spill concerns since there is no acid in the component. See also List of battery types List of battery sizes Comparison of battery types Nickel–zinc battery References Iron battery Iron Rechargeable batteries