= End-of-life criterion
An <end-of-life criterion> specifies the condition at which a component is treated as having exhausted its useful operation for a stated purpose. It supplies the endpoint needed to define <remaining useful life>. The criterion may be a performance threshold or an observed failure condition; useful operation can end before complete physical destruction. Its units, measurement procedure and operating conditions belong in the specification.
A primary NASA battery-aging test used30% loss of rated capacity, from2Ah to1.4Ah, as the aging endpoint. The apparatus separately used terminal-potential limits to finish individual discharges. Those two endpoints describe different processes and timescales.<Li-ion Battery Aging Datasets by NASA>[Dataset description, discharge termination and aging end-of-life criterion]{ref} A prediction stated only as “time until the battery ends” would therefore omit an essential physical definition.
For an illustrative linear capacity model, suppose present capacity is1.8Ah and future fade is0.01Ah per cycle. A1.4Ah end criterion gives40 remaining cycles, whereas a1.2Ah criterion gives60. The assumed degradation path is unchanged; the endpoint definition changes the reported lifetime. The example thresholds and rate are hypothetical, rather than a recommendation or a fit to the NASA data.
<Competing end-of-life criteria> also need a logical rule. If operation ends when either limit is first reached, the lifetime is $R=\min(R_1,R_2)$. Threshold crossings at12 and20h then give12h. A rule requiring both limits to be exceeded would define another event. Recording the criterion before evaluating a prediction avoids changing the target after observing the result, and supports an interpretable <remaining-life validation error>.
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