Lithium-ion (LiOn) batteries can handle hundreds of charge/discharge cycles, don't suffer from the memory effect, hold a charge better, work at higher voltages, are more compact and are lighter than nickel-cadmium (NiCad) batteries. However, they are more expensive and aren't available in standard sizes.
Because NiCad batteries have a self-discharge rate of 15 to 20 percent per month, they are unsuitable for long-life applications that require low power. LiOn batteries have a self-discharge rate of 2 to 8 percent per month, which makes them ideal for products that require a long battery life. If a person does not fully discharge a NiCad battery every time he uses it, the battery loses capacity by charging to a 'remembered' level lower than full capacity with every subsequent charge, an issue known as the memory effect.
NiCad batteries can deliver high currents without suffering damage or losing capacity thanks to their low internal resistance. This makes them suitable for high-current applications such as remote-controlled cars and aircraft. NiCad batteries contain cadmium, a toxic heavy metal that is harmful to the environment, whereas LiOn batteries are more environmentally friendly. In addition NiCad batteries require more maintenance and are more difficult to charge than LiOn batteries. They require occasional cycling to prevent capacity loss and are vulnerable to overcharging. LiOn batteries don't require cycling and come with chargers that prevent overcharging.