Battery Cycling Testing Explained
Observing capacity fade, efficiency trends, and impedance growth over hundreds or thousands of charge-discharge cycles — the primary method for simulating long-term battery field use.
How Battery Cycling Testing Works
From procedure design to fade analysis — a practical guide to running and interpreting long-cycle battery programs on automated test systems.
What Battery Cycling Testing Is
Battery cycling testing applies repeated charge-discharge cycles to a cell or pack under controlled conditions, tracking how performance changes over time. The core outputs — capacity per cycle, energy per cycle, efficiency, and internal resistance — reveal how the battery ages and when it will reach its end-of-life threshold. Cycling tests are the primary tool for lifetime prediction, warranty support, and product comparison.
Building a Cycling Procedure
A typical cycling procedure uses a Do/Loop structure to repeat a charge-rest-discharge-rest sequence for a defined number of iterations:
- Do step: set the number of cycles (up to 32,000 per loop; loops can be nested).
- Charge step: CC-CV charge to the upper voltage limit, ending when current tapers to a threshold.
- Rest step: open-circuit rest for a defined period to allow voltage relaxation.
- Discharge step: constant current discharge to the lower voltage cutoff.
- Rest step: post-discharge rest before the next cycle begins.
- Loop step: returns execution to the Do step for the next cycle.
- End step: terminates after all loops complete or a cycle-count end condition is met.
What to Measure During Cycling
MIMS Client cycle-based charts can plot any of these metrics against cycle number:
- Charge and discharge capacity (Ah): Primary fade indicator.
- Charge and discharge energy (Wh): Captures voltage-profile changes over life.
- Coulombic efficiency: Discharge Ah ÷ Charge Ah per cycle — sensitive to side reactions.
- DC Internal Resistance (DCIR): Measured from pulse steps embedded in the procedure.
- Mean discharge voltage: Tracks voltage depression as the cell ages.
- Terminal rest voltage: Open-circuit voltage after rest — indicator of SoC and health.
Where Cycling Tests Add Value
Cycling is used at every stage — from early chemistry screening to production qualification and field reliability work.
| Environment | Primary Goal |
|---|---|
| R&D Laboratories | Compare electrolyte formulations and electrode designs |
| Validation Programs | Verify cycle life against warranty and specification targets |
| Production & QA | Detect lot-to-lot variation before shipment |
| Reliability & Aging | Build statistical models of capacity fade and failure modes |
Benefits for Engineers and Technical Buyers
Automated cycling tests eliminate manual intervention and ensure consistency across long programs.
- Unattended operation: Fail-safe channel behavior protects cells and equipment if limits are exceeded.
- Reference performance tests (RPT): Insert periodic low-rate capacity checks within a loop to track fade cleanly.
- Suspend-Modify-Restart (SMR): Safely edit procedures mid-test without losing accumulated data.
- MIMS Server archiving: Automated ASCII export after each test for long-term data management.
Frequently Asked Questions
How many cycles can a Maccor procedure loop?
A single Do/Loop structure supports up to 32,000 iterations. Nested loops multiply this limit — two nested loops can execute up to 32,000² cycles before requiring a new test start.
How do I capture DCIR during a cycling test?
Insert a short pulse discharge step (or pulse charge step) at the start of each cycle. The voltage response to the current pulse, divided by the current magnitude, gives the DC internal resistance at that state of charge.
What is the EndOnCycle step type used for?
EndOnCycle terminates the test automatically when a specified cycle count is reached, without requiring the loop count to be set in advance. It is useful when end-of-life is defined by a capacity threshold rather than a fixed number of cycles.