Reliability of Primary Batteries: A Case History

Evaluation of the reliability of a primary battery took place in three stages: 1) 192 batteries went through a slow-discharge test. 2) A designed experiment was conducted on 144 batteries; there were three factors in the experiment: storage temperature (three levels), thermal shock (two levels), and date code (two levels). 3) 16 batteries experienced a cycled temperature and humidity environment. All tested batteries showed acceptable performance. Results of the designed experiment showed the factor most affecting battery performance was the date code. A long-term capacity test on a sample of primary batteries can provide information on their quality and reliability. The example shows a very tight capacity distribution. The battery employed a lithium anode. The capacity of many lithium-based battery systems is, by design, limited by the quantity of lithium in the anode. Controls on that quantity may permit the manufacturer to control, with considerable precision, the capacity of the batteries. From the designed experiment, we infer that the factor most affecting the performance of the battery is the time when it was made. Long term storage, perhaps up to 10 years, in a ``normal'' environment of 20° C will not appreciably affect it, nor will thermal shock or 2-way combinations of factors. Three way interactions were not examined. Some batteries went through a temperature-and humidity-cycling. The capacity of these batteries, after test, met the requirements of the specification.