BU-922: What Causes Starter Batteries to Fail?

A new battery starts service at an expected capacity of 100%. With use, the capacity fades until the battery can no longer deliver the required energy to crank the engine and motorists get stranded. This article introduces a test method assessing the remaining useful life of a battery.

A starter battery is rated in RC (Reserve Capacity) in minutes applying 25A discharge; however; the global IEC standard is in Ah (ampere hour) discharging a battery at 0.2C-rate, also called the 5-hour discharge.

Screenshot 2026 04 09 222057 — *Assessing the remaining useful battery life*

Besides delivering energy, a starter battery also supplies power that reaches 300A during cranking, measured in CCA (Cold Cranking Amp). SAE J537 standards measures CCA by applying a load equal to the CCA rating while the battery is cooled to -18°C (0°F). To pass, the voltage must stay above 7.2V for 30 seconds under load. IEC standards vary voltage levels and timing at cold state.

Statistics reveal that 48% of starter batteries fail by capacity fade while only 12% quit by low CCA. Modern battery test devices assess capacity by Multi-Model EIS available in Spectro™ by Cadex.

A non-invasive frequency scan creates a Nyquist plot that is modeles against a matrix to assess capacity, CCA and state-of-charge (SoC). Accuracy is governed by the Matrix Integrity Level (MIL) that can be improved by scanning additional batteries of same mode but various state-of-health conditions. Test time is 30 seconds, longer with very large batteries.

Spectro devices tests a battery to validate Minimum Operational Reserve Energy (MORE). The pass/fail capacity on starter batteries on cars is typically set to 40%; trucks with hotel load may select a matrix with 50%. MORE. PASS gives a grace period to next service while FAIL calls for replacement even if cranking is still strong. Focus is on capacity assessment.

The Spectro CM-24 comes with a matrix of choice. Other matrices can be downloaded from the Matrix Library by the CadexCloud, a web app that also stores test results and notes vehcile number to share with users.

Batteries in commercial vehicles can be QR-coded to review historic reading and download model-specific matrices with scanning. This turns the Spectro™ rapid-tester into an open platform to service virtually any battery.

A generic matrix checks starter batteries in consumer auto while custom matrices service large vehicles, machinery and marine vessels. The device also tests deep cycle batteries in lead acid and lithium-based chemistries.

Connectivity

Settings are entered by the host with test results shown in numbers and by graphics. The system works in local mode by storing data in the host with optional connectivity to CadexCloud to share test results with fleet supervisors.

Stored information includes pass/fail status, state-of-charge, internal battery resistance and temperature, as well as VIN numbers and work orders. With compatible printer, printing reports and labels can be produced.

How do Batteries Age?

The graph on the right reflects capacity fade of 175 starter batteries tested by a German luxury car maker. Capacity loss follows the arrow in passing through the Capacity End-of-life gate while most CCA readings remain in operating range. A CCA test alone is incomplete.

*175 starter batteries are tested according to SAE J537*

Capacity assessment with multi-model EIS is of special interest when testing large batteries of up to 300Ah, enabled by EIS Direct Drive. Furthermore, the SoC range for starter batteries has been extended down to 50%.

*Percentage of offering roadside assistance*

Reports by ADAC (Allgemeiner Deutscher Automobil-Club) in Germany record the most frequent cause of roadside help provided. Throughout the years, the battery remains the weakest link in a vehicle with 45% of all calls being battery related. In comparison, motor management, alternators and tires are less than half. This in spite of modern BMS that often give false battery fail indications but are unable to assess battery capacity, the leading health indicator.

Most battery testers check CCA by a load test that cannot give accurate stat-of-health readings. CCA tends to stay high while capacity drops predictably to below workable levels without knowing.

Scientists envision the future of battery diagnostics in EIS, a technology that Spectro CM-24 deploys, but has not yet been fully explored.

Spectro™ Characteristics

Battery rapid-testing with multi-model electrochemical impedance spectroscopy using frequency scanning with AI analysis delivers impressive results. Typical scanning frequencies range from 2,000Hz to 4Hz for most batteries with option to go lower if time allows. Common test voltages are 3V to 48V with capacity assessment of up to 300Ah provided the internal battery resistance is above 300µΩ.

Last Updated: 9-Apr-2026

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The material on Battery University is based on the indispensable new 4th edition of "Batteries in a Portable World - A Handbook on Rechargeable Batteries for Non-Engineers" which is available for order through Amazon.com.

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