Nickel-iron battery
The nickel–iron battery (NiFe battery) are batteries made of iron and nickel oxide hydroxide, with a potassium hydroxide electrolyte. They are very strong, and do not break easily. They can last for more than 20 years. They are slow to charge. They are often used on trains. They are similar to the nickel cadmium battery, but using iron instead of toxic cadmium. The voltage is 1.2 volts per cell, the same as the nickel cadmium battery.