Lithium batteries were designed for use in digital cameras and similar low discharge rate consumer electronics. The cell has the advantage of high energy density compared to more traditional battery chemistries (such as alkaline). The batteries are stable in a wide range of temperatures and have a shelf life of 10 years. However, when used in devices such as high intensity flashlights which have a high rate of discharge, internal cell heat can build up. This can result in explosive conditions. The Duracell Battery Company developed the first re-settable current and Thermal Protection System. All ASP batteries incorporate a similar PTC (Positive Thermal Coefficient) device and pressure relief vent. If an ASP battery short circuits or discharges at currents above their design limit, the PTC causes the cell's internal resistance to increase, limiting the amount of current that can be drawn and keeping the internal cell temperature within safe limits. The pressure relief vent activates and relieves excessive internal pressure. These internal safety devices increase battery cost. When using Lithium batteries in a high discharge rate device such as a flashlight, always insist on PTC batteries.
A PTC circuit and backup pressure relief vent allow safe operation of AAA Lithium batteries in high discharge devices such as high intensity LED flashlights.