Lithium ion cells packaged in aluminium cans continue to be the highest performing cells in the market. Circuit protection for rechargeable lithium-based battery cells and packs in a critical design consideration. overcurrent and overtemperature conduction that can result from accidental shorting or abusive/runaway charging can raise temperature high enough to damage components and cause substantial damage. This paper presents the use of PPTC devices for short-circuit and overcharge of battery packs. Polymeric positive temperature coefficient [PPTC] devices help to protect circuits by going from a low-resistance state to a high resistance state in response to an overcurrent or overtemperature condition. Commercially available OEM packs with Li-P and Li-Mn cells are now employing PPTC devices for primary protection. Laboratory overcharge testing at 25°C,12V demonstrated that PPTC devices reduced maximum cell temperature by 40°-50°C, while also helping to prevent bulging, rupture, seperator melting and cell shut down. Ultimately, pack designers must decide what level of protection is required for their application and only a system test can determine whether or not a specific protection device is appropriate. PPTC devices have demonstrated their effectiveness in a wide range of circuit protection applications .Their ability to provide reliable, resettable protection reduces costly warranty returns and improves user satisfaction.