The present invention pertains to a battery comprising an anode comprising iron sulphide as active material, with the sulphur content being at least 5 wt.% of the total of iron and sulphur, a cathode, and an alkaline electrolyte comprising an alkaline component dissolved in water, with the anode comprising less than 0 wt.% of other active materials than iron sulphide. Preferably, the sulphur content of the anode is more than 10 wt.% of sulphur, calculated in the total of iron and sulphur and 70 wt.% or less. It has been found that the use of iron sulphide in the anode provides a rechargeable electrical energy storage system which is low-cost, easy to produce, and environmental friendly, and which shows a long lifetime and has excellent electrochemical properties like high power density and good cycling efficiency. The battery according to the invention also shows superior charge/discharge behavior as compared to e.g. lead-acid and nickel-iron batteries.