ADL Embedded Solutions CMOS batteries (p/n 100-9655) are based on a 3.6V Lithium Thionyl Chloride battery, with a 100k ohm, 5%, ¼W, current limiting resistor installed to protect battery life. The resistor provides a voltage drop for a 10uA or smaller load so that the 3.6V potential does not produce excessive on-state current. Current does flow from the battery in the ON state. It is significantly less with the resistor. If no resistor was used, damage to the circuitry could occur, and the battery drain in the ON state would exceed that in the OFF state.

Most modern chipsets can keep the RTC running with less than 10uA of current from the battery, with 6uA being a typical requirement. Using the 1.20Ah rating of the battery, the life expectancy would be 1.2A/6uA = 200,000 hours, or about 22 years at +20°C. Considering that the self-discharge of the battery is <1% per year at +20°C, it is reasonable to expect that the useful life of the battery is indeed, >10 years. For serviceable applications, we suggest a 5 year service interval, in general. Regardless of the ideal time interval or operating conditions, CMOS batteries sold by ADL Embedded Solutions are mass produced and not rechargeable. ADL Embedded Solutions recommends that all developers include connectors and/or clips in their system design so that their CMOS battery can be easily replaced in the field.