Estimating Real Time Lifespan of Nonrechargable Coin Cells by Parameter Measurements

Abstract

Primary batteries are used in many commonly used devices like clocks, wrist watch, toys, pocket calculators, hearing aid, flashlight, radios and home equipments. Special primary batteries are used in medical equipments, missiles, and weapon systems. The lithium-manganese dioxide primary cells, also called as coin cells, usually 3V, are most commonly used lithium primary cells. Now, as these cells are used in wide variety of applications, it is important to know some of their characteristics. We all know that whenever any battery is used in a product, its capacity decreases with time and use. As soon as these cells are installed in a device, or a load is connected across them, they start discharging. But the exact time taken by the battery to discharge completely is not known while connecting the load. Hence, it is difficult to tell how long the battery works; hence we cannot estimate how long a product which uses coin cell to power itself, will last. The paper aims to concentrate on calculating real time lifespan of a nonrechargeable coin cell. The coin cells are discharged using different loads across them. During each discharge, battery voltage, load current, internal resistance and battery capacity are measured. By this discharging process an experimental discharge time is known. Using these experimental discharge times and battery parameters for each load, a relation is established between the battery parameters to find the battery capacity. Using this calculated capacity, battery lifespan is calculated.