Battery degradation is only visible when three data streams are read together: BMS telemetry (voltage, current, temperature per rack), cycle and throughput history, and periodic thermal or visual inspection. Any one stream alone will mislead you, because state of health is a pattern, not a number.
Why state of health is not one number
Every battery management system computes state of health differently, and most vendors treat the method as proprietary. Two identical containers from two suppliers can report 92 percent and mean very different things. Comparing racks, let alone sites, requires normalizing to a common definition before any trend is trustworthy.
The three streams that matter
BMS telemetry shows how the asset behaves day to day: cell imbalance, temperature spread, charge windows. Cycle data shows cumulative wear: equivalent full cycles, depth of discharge, rest periods. Thermal and visual inspection shows the physical state: hot spots, swelling, connection damage. Gridledger ingests all three, from any BMS vendor or inspection provider, and aligns them on one timeline per rack.
What operators gain from one timeline
When telemetry, cycles and inspection sit on one open timeline, warranty claims stop being arguments. You can show exactly when a rack diverged, what the operating conditions were, and which inspection confirmed it. That record belongs to you, is stored in an open format, and stays readable long after any vendor dashboard is switched off.