{ "node": { "id": "term:cell-to-cell-variation", "type": "Term", "label": "Cell-to-cell variation", "properties": { "id": "cell-to-cell-variation", "name": "Cell-to-cell variation", "section": "topic-state", "definition": "The spread in capacity, resistance and self-discharge between nominally identical cells, from manufacturing and from unequal temperatures in service. It is why packs need balancing and why grading matches cells before assembly.", "related": [ "cell-balancing", "grading", "end-of-line-testing", "thermal-management" ], "url": "https://lemonergy.com/learn/glossary/cell-to-cell-variation/", "mentions": [ "self-discharge" ] } }, "edges": [ { "id": "edge:1337", "source": "term:cell-to-cell-variation", "target": "topic:topic-state", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:1338", "source": "term:cell-to-cell-variation", "target": "term:cell-balancing", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1339", "source": "term:cell-to-cell-variation", "target": "term:grading", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1340", "source": "term:cell-to-cell-variation", "target": "term:end-of-line-testing", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:1341", "source": "term:cell-to-cell-variation", "target": "term:thermal-management", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:mentions/cell-to-cell-variation/self-discharge", "source": "term:cell-to-cell-variation", "target": "term:self-discharge", "type": "mentions", "properties": { "sourceFile": "terms.json", "method": "build_glossary.mention_index + mentions", "field": "definition", "meaning": "Text mention; not a causal claim" } }, { "id": "edge:1343", "source": "term:cell-to-cell-variation", "target": "visual:balancing", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } } ], "neighbors": [ { "id": "topic:topic-state", "type": "Topic", "label": "State estimation", "properties": { "id": "topic-state", "name": "State estimation", "lede": "The quantities a battery management system estimates but cannot measure directly.", "context": "Distinguish internal states from noisy measurement estimates.", "example": "Current-sensor bias accumulates in coulomb counting. Exact model SOC does not establish real estimator accuracy.", "lesson_url": "https://lemonergy.com/learn/fundamentals/capacity-and-c-rate/", "lesson_label": "Open charge balance" } }, { "id": "term:cell-balancing", "type": "Term", "label": "Cell balancing", "properties": { "id": "cell-balancing", "name": "Cell balancing", "section": "topic-state", "definition": "Equalising the state of charge of cells in series, since the pack is limited by its emptiest cell on discharge and its fullest on charge. Passive balancing bleeds charge from high cells through resistors; active balancing moves it between cells.", "related": [ "bms", "series-parallel", "state-of-charge", "cell-to-cell-variation" ], "example": { "title": "Pack average versus cell limits", "text": "Average pack SOC can look acceptable while one series cell reaches its voltage limit. One aggregate SOC state does not demonstrate cell balancing." }, "url": "https://lemonergy.com/learn/glossary/cell-balancing/", "mentions": [ "active-balancing" ] } }, { "id": "term:grading", "type": "Term", "label": "Grading", "properties": { "id": "grading", "name": "Grading", "aka": [ "binning", "sorting" ], "section": "topic-manufacturing", "definition": "Sorting finished cells into bins by capacity and resistance so a module is built from closely matched cells. Mismatched cells would force the pack to balance constantly and age its weakest cell fastest.", "related": [ "end-of-line-testing", "cell-to-cell-variation", "cell-balancing" ], "example": { "title": "State the sorting criterion", "text": "Cells in the same capacity band can differ in resistance. One grading criterion does not establish uniformity in every property." }, "url": "https://lemonergy.com/learn/glossary/grading/", "mentions": [ "weakest-cell" ] } }, { "id": "term:end-of-line-testing", "type": "Term", "label": "End-of-line testing", "properties": { "id": "end-of-line-testing", "name": "End-of-line testing", "abbr": "EOL test", "section": "topic-manufacturing", "definition": "The final measurements on every finished cell — capacity, internal resistance and open-circuit voltage — used to reject faulty cells and sort good ones into matched grades.", "related": [ "grading", "capacity-test", "k-value", "cell-finishing" ], "lesson": "fundamentals/cell-production/#finishing", "url": "https://lemonergy.com/learn/glossary/end-of-line-testing/", "mentions": [ "internal-resistance", "open-circuit-voltage" ] } }, { "id": "term:thermal-management", "type": "Term", "label": "Thermal management", "properties": { "id": "thermal-management", "name": "Thermal management", "abbr": "TMS", "aka": [ "battery thermal management system", "BTMS" ], "section": "topic-thermal", "definition": "Keeping cells in their comfortable range, roughly 15–35 °C, and within a few degrees of each other: liquid cooling plates, refrigerant plates or immersion for heat removal, and heaters or waste heat for warming before fast charging in the cold.", "related": [ "cooling-plate", "thermal-interface-material", "operating-temperature", "heat-generation", "preconditioning", "temperature-sensor" ], "url": "https://lemonergy.com/learn/glossary/thermal-management/", "mentions": [ "fast-charging" ] } }, { "id": "term:self-discharge", "type": "Term", "label": "Self-discharge", "properties": { "id": "self-discharge", "name": "Self-discharge", "section": "topic-charging", "definition": "The slow loss of stored charge while a cell is not in use. An unexpected rise can signal a leakage path or a soft internal short.", "unit": "%/month", "related": [ "internal-short-circuit", "calendar-aging", "k-value", "calendar-life", "self-discharge-test" ], "lesson": "fundamentals/battery-aging/#check-yourself", "url": "https://lemonergy.com/learn/glossary/self-discharge/", "mentions": [] } }, { "id": "visual:balancing", "type": "Visual", "label": "The limiting cell matters", "properties": { "title": "The limiting cell matters", "summary": "A pack average can hide a cell that reaches its voltage limit first.", "readout": "Average: 3.93 V. Highest cell: 4.02 V. The highest cell can reach the charge limit first.", "formula": "V_max = max(V₁, V₂, …); V_average = ΣV_i / N", "note": "The 4.2 V ceiling is an example, not universal. Voltage alone does not uniquely determine SOC.", "software": { "status": "reference", "label": "Reference concept", "body": "Cell supervision uses individual voltages. The native Studio battery is an aggregate model; this chart does not claim it simulates cell balancing.", "href": "https://design.lemonergy.com/cosim.html?example=charging-home" }, "html": "
Four cells before balancing
Four cells before balancingCell number versus Cell voltage (V). Individual voltages; Average; Example ceiling. Interpretation follows the graphs.3.713.851.7542.54.153.254.34Cell numberCell voltage (V)
Individual voltagesAverage (dashed)Example ceiling
" } } ] }