The reference capacity test
State of health, as we use it, is measured usable capacity expressed as a percentage of rated capacity. We measure it with a full constant-current charge and discharge cycle at a standard rate and controlled temperature, after allowing the module to rest and reach thermal equilibrium.
Using the same rate, temperature and voltage limits for every module of a given type makes results comparable across batches, sites and time. Changing any of these conditions can shift the measured capacity, so procedures are fixed and documented.
Beyond capacity
Capacity tells us how much energy a module holds, but not how well it delivers it. DC internal resistance, measured with a current pulse, shows how much voltage drops under load and how much heat the module generates. Rising resistance often signals ageing that capacity has not yet revealed.
Where more detail is needed, electrochemical impedance spectroscopy separates different contributions to resistance, helping identify degradation mechanisms. Combined with thermal observations during testing, these measurements support both grading and matching decisions.
- Full-cycle capacity at standard rate and temperature
- DC internal resistance from pulse testing
- Impedance spectroscopy where detail is needed
- Temperature logging throughout the test
From measurement to grade
Results feed directly into our grading bands: grade A at 85% or above, grade B from 75% to 85%, grade C from 65% to 75%, with grade D routed to refining. Resistance, impedance and physical inspection can move a module down a grade even when capacity looks acceptable.
Every result is stored against the module's serial number, along with test conditions and equipment calibration records. That record supports settlement, warranty terms for second-life buyers and the owner's own reporting.
Field note