Lithium cell model Li-polymer battery 18650 lion battery Voltage of single cell of lithium polymer battery is 3.7v, but ni-mh and ni-cd is only 1.2v, which means one lithium battery cell could replace three ni-mh or ni-cd cells. Therefore, lithium battery pack has much smaller size than ni-mh and ni-cd battery pack. Self-discharge rate of lithium battery is 5% per month, which is much lower than ni-mh and ni-cd (25% per month). Lithium battery has around 800 times of cycle life, which is also longer than ni-mh and ni-cd(500 times). So lithium battery is replacing ni-mh and ni-cd in more and more fields.