A car battery comprises: four lithium ferro-phosphate batteries serially connected and positioned within a battery case with the anode and cathode caps exposed and connected to each other, and each of the lithium ferro-phosphate batteries has a capacity of 10-20 ampere-hour. The car battery also comprises two wires respectively connected to the anode and cathode caps, and the wires are thus connected to the anode and cathode of the lithium ferro-phosphate batteries connected in series.