The Patent Landscape: 60+ Filings, One Central Problem

The central technical problem addressed across more than 60 active and pending filings — spanning Korea, Japan, Europe, and Australia — is that large-format battery modules accumulate divergent charge states, degradation rates, and internal resistances across constituent cells and banks, eventually reducing usable capacity to that of the weakest element in the series chain. The dominant technical domains in this corpus cover state-of-charge (SOC) estimation, cell and module balancing circuits, internal resistance diagnosis, and anomaly detection algorithms.

LG Energy Solution (including its predecessor LG Chem) is the most prolific assignee by volume, with more than 25 patent filings covering the full spectrum from SOC/SOH estimation to hierarchical rack-level BMS architectures. Samsung SDI, SK On, Robert Bosch GmbH, Korea Electrotechnology Research Institute, Linear Technology LLC (now part of Analog Devices), and Sungrow Power Supply round out the principal contributors. Together, these organisations have systematically documented — and patented solutions to — every major mechanism by which battery packs degrade in capacity uniformity over their operational lifetimes.

The filings span applications in electric vehicles (EVs), grid-scale energy storage systems (ESS), and industrial battery packs. What unites them is the recognition that a series-connected string of cells or modules is only as capable as its weakest member — and that without active intervention, divergence compounds over time through a combination of electrochemical, mechanical, and thermal mechanisms.

Four Root Causes Driving Capacity Imbalance

Capacity imbalance in large-format battery modules arises from four distinct but interacting mechanisms, each of which operates on a different timescale and requires a different detection strategy.

Manufacturing Variation and Cell-Level Parameter Spread

Even within tightly controlled production batches, individual cells exhibit differences in internal resistance, electrode coating uniformity, and electrolyte distribution. These initial differences are small but consequential: as demonstrated by SK On’s 2021 BMS patent, SOC divergence within a pack emerges progressively as cells with varying state-of-health (SOH) respond differently to identical charge and discharge currents. The system selects “high-risk group battery cells” by applying SOH-dependent corrections to each cell’s SOC, explicitly acknowledging that a single representative SOH value inadequately captures inter-cell heterogeneity. Robert Bosch GmbH formalises this by computing a quality factor for each cell that combines a function of state of charge with a function of the product of current and internal resistance — explicitly coupling electrical state with electrochemical aging.

Differential Self-Discharge

Cells with manufacturing defects, micro-short circuits, or contamination discharge faster during rest periods than neighbouring cells, producing SOC divergence even without any applied load. BMW’s 2021 patent addresses this directly by monitoring balancing charge per cell over time, enabling prediction of safety-critical internal short circuit conditions well before thermal or voltage anomalies become detectable. LG Energy Solution’s detection of lithium precipitation calculates cumulative deviations between measured terminal voltage and open-circuit voltage (OCV) to flag cells undergoing abnormal electrochemical processes such as lithium plating.

“Self-discharge monitoring via per-cell balancing charge tracking enables early detection of internal short circuits before voltage-level anomalies are detectable — providing a critical safety margin for large-format packs.”

Contact Resistance Asymmetry and Interconnect Degradation

In large-format packs consisting of parallel battery banks, contact resistances at bus bars and connectors vary across banks, causing unequal current distribution. LG Energy Solution’s 2023 battery management patent specifically decomposes measured bank voltages into internal resistance components and external contact resistance components, then calculates compensated bank voltages by removing the voltage drop due to each contact resistance. This compensation is necessary because raw voltage measurements taken at module terminals misrepresent actual cell SOC when resistance is non-uniform. The same methodology appears across multiple LG Energy Solution patent families including a 2026 filing, confirming this as a persistent, systematically addressed engineering challenge.

Thermal Gradients

In large-format modules, cells positioned near the centre experience higher operating temperatures than edge cells, accelerating electrochemical aging and increasing local self-discharge. A 2021 hierarchical management patent deploys temperature sensors at designated locations throughout each module and aggregates temperature values across all sub-management modules to the main management module, explicitly managing both voltage balance states and temperature balance states simultaneously. SoluM’s 2024 battery pack device extends this architecture to commercial pack designs, confirming that dual-domain monitoring of temperature and capacity imbalance has become standard in production-grade systems.

BMS Algorithms for Detection and Correction of SOC Imbalance

BMS algorithms addressing capacity imbalance operate across three functional tiers: measurement and state estimation, fault detection and diagnosis, and active or passive equalization control. Each tier depends on the accuracy of the one below it — a balancing decision made on inaccurate SOC data can worsen the imbalance it is intended to correct.

SOC and SOH Estimation as the Foundation

Without accurate per-cell or per-module SOC, balancing decisions are uninformed and may over-discharge weak cells. LG Chem’s 2016 battery management patent implements a SOC/SOH estimation loop that triggers a balancing signal when maximum SOC deviation across modules reaches a first limit deviation, and escalates to a diagnostic signal at a second, higher limit deviation. Critically, when modules are replaced with new units having different SOH than the original pack, the algorithm applies a corrected third limit deviation proportional to the SOH deviation between old and new modules — preventing false alarms in heterogeneous-age packs. Samsung SDI’s 2024 approach uses an adaptive filter to update G and H parameters in real time from voltage and current measurements, where G represents voltage sensitivity to current change and H captures the effective potential from local equilibrium potential distribution and resistance distribution, enabling model-based SOH estimation without full-cycle testing requirements.

Voltage History Analysis and Anomaly Detection

LG Energy Solution’s 2024 battery management system constructs an observation matrix of voltage vectors measured in a sliding time window for each cell, then generates a restoration matrix of predicted voltage vectors. Differences between observed and restored vectors are used to detect abnormality — cells with internal short circuits or abnormal self-discharge produce reconstruction errors that differ statistically from the healthy population. SK On’s 2021 system uses maximum voltage change rate across cells to select high-risk candidates and calculate a maximum current limit value that keeps all cells within their operating voltage window, providing a safety constraint derived directly from inter-cell imbalance severity.

Statistical Delta-SOC Methods for Internal Short Circuit Detection

Internal short circuit detection via SOC change tracking has emerged as a specialised sub-algorithm for identifying the most dangerous form of self-discharge imbalance. LG Energy Solution’s 2022 patent applies a SOC estimation algorithm during charging, computes the first SOC change (delta-SOC between two charge time points) for each cell, then applies a statistical algorithm to the ensemble to derive a reference factor. Cells whose delta-SOC deviates from the reference factor are flagged for internal short circuit. This statistical reference approach is robust against pack-wide aging because it normalises each cell’s delta-SOC against its peers, making the detection relative rather than absolute — a critical design choice for large cell counts where absolute SOC accuracy is difficult to maintain.

Resistance Degradation Pulse-Discharge Diagnosis

Progressive increase of internal resistance in aged or degraded cells generates unequal ohmic voltage drops under load, causing apparent SOC imbalance even when true charge states are equal. LG Energy Solution’s 2023 resistance degradation diagnosis patent implements a pulse discharge protocol on target battery banks, recording bank voltage before and after discharge, deriving the current voltage change amount, and comparing it against a stored reference voltage change amount to estimate resistance degradation degree. This approach enables non-intrusive, in-service resistance mapping without requiring electrochemical impedance spectroscopy (EIS) hardware — a significant practical advantage for deployed packs. A 2025 extension estimates internal resistance of parallel-connected modules from routine voltage and current measurements, setting a reference resistance from the ensemble and flagging modules deviating beyond a defined threshold.

Balancing Circuit Topologies: From Passive Resistors to Hierarchical Rack Control

BMS algorithms require corresponding hardware to execute calculated balancing commands. The patent dataset reveals a spectrum of passive, active, and hybrid circuit approaches, each with distinct trade-offs between cost, efficiency, and scalability.

Passive Balancing via Resistive Dissipation

Passive balancing remains the baseline approach for cost-sensitive applications. Korea Electrotechnology Research Institute’s 2014 patent establishes the canonical passive algorithm: measure OCV for each cell, designate a balancing voltage from the measured set, and discharge cells above this voltage through switch-controlled resistors until all OCVs converge. While thermally inefficient, this approach is reliable and simple. LG Chem’s 2019 patent adds thermal management integration, routing current from the balancing resistor through a fan cooling circuit and using second switching units to manage the thermal load generated during passive balancing — addressing a practical limitation of resistive dissipation in high-energy modules. Standards bodies including IEC define safety requirements for the thermal management of such dissipative circuits in large-format applications.

Active Balancing with Equalization Current Injection

Active balancing transfers charge rather than dissipating it, achieving higher energy efficiency. LG Chem’s 2020 apparatus and method implements a Cell Module Controller (CMC) for each battery module and a central Battery Module Controller (BMC) that calculates SOC for each module, diagnoses abnormal modules, and forms a closed equalization current supply circuit connecting the BMC to the target module via switching units. The position of the abnormal module within the string determines which switching units are activated to route equalization current optimally. LG Energy Solution’s 2024 apparatus introduces a dedicated balancing line, electrically independent from the main power line, that connects positive and negative terminals of multiple cell assemblies in parallel — enabling continuous balancing during charge and discharge operations without interrupting the main current path.

Constant Current Balancing with DC/DC Conversion

Crest Co., Ltd.’s 2022 patent uses a single charging control unit and a single discharging control unit sharing DC/DC converters for each direction, with a switching unit that reconfigures the current path to connect the appropriate converter to the target cell. This topology reduces converter count relative to per-cell active balancing architectures, lowering cost while preserving bidirectional energy transfer capability.

Voltage-Compensated Active Cell Balancing

Linear Technology LLC’s 2016 patent addresses a fundamental measurement accuracy problem: cell voltage measured during a balancing current flow is distorted by the ohmic drop across series resistance. The apparatus measures both cell voltage and the voltage drop due to balancing current, then calculates a corrected open-cell voltage by subtracting the ohmic contribution. Balancing decisions are then based on this corrected OCV rather than the raw measured voltage, significantly improving balancing accuracy at high currents. Samsung SDI’s 2026 battery management system applies a similar connection-resistance correction during voltage measurement to improve both measurement precision and balancing efficiency. Research published by IEEE has extensively documented the measurement errors that arise from ohmic drop during active balancing and the accuracy gains achievable through compensation.

Hierarchical BMS Architecture for Large ESS Packs

LG Energy Solution’s 2024 hierarchical BMS patent employs a Rack BMS (RBMS) as the first-level management device that determines whether balancing execution conditions are met based on idle state and charging status, sets balancing targets and timing, and commands Pack BMS (PBMS) units residing within each Battery Module Assembly (BMA). The PBMS executes cell-level balancing according to RBMS instructions. This design cleanly separates system-level strategy from module-level execution and scales to large ESS rack configurations. The same hierarchical design principle is embodied in a 2021 patent from inventor Kim Chang-in, which implements distributed sub-management modules reporting to a central main management module.

Bypass and Fault Isolation

When a module’s imbalance is severe enough to threaten pack integrity, bypass circuits provide a protective corrective action. Thunder Power New Energy’s 2018 patent implements a connecting circuit that normally places each module in series but, upon detection of abnormal operation, disconnects the defective module and directly bridges the preceding and succeeding modules, maintaining series circuit continuity. This hardware bypass function complements BMS diagnostic algorithms by providing a graceful degradation path when balancing alone cannot restore pack operability — a design approach increasingly relevant as battery packs scale to multi-megawatt-hour ESS installations, as documented in reports from IRENA.

Key Players and the Shift Toward Statistical, Model-Based Anomaly Detection

The patent landscape reveals both a clear hierarchy of innovation leadership and a directional shift in how imbalance is detected — from fixed voltage thresholds toward statistical and model-based methods that adapt to pack aging without recalibration.

Assignee Profiles

LG Energy Solution / LG Chem dominates the dataset with more than 25 patent filings across SOC/SOH estimation, active balancing circuits, internal resistance diagnosis, short circuit detection, contact resistance compensation, and hierarchical BMS architectures. Their intellectual property portfolio spans Korea, Japan, and international jurisdictions, reflecting global deployment in EV and ESS markets.

Samsung SDI contributes to both SOH estimation methodology through adaptive G/H parameter filters and cell balancing hardware, with recent filings addressing connection-resistance correction and RC-circuit fault compensation in BMS balancing switches.

SK On focuses specifically on high-risk cell identification and current limit management, producing BMS algorithms that select cells most likely to exit operating voltage bounds and use these as the basis for conservative current limiting rather than aggressive balancing.

Robert Bosch GmbH approaches the problem from a probabilistic switching standpoint, computing quality factors that incorporate both SOC and the product of current and internal resistance to determine connection probabilities for individual cells, enabling dynamic reconfiguration of the series string to compensate for inter-cell variation.

Korea Electrotechnology Research Institute and Linear Technology LLC have contributed foundational balancing methodologies — OCV-based passive equalization and voltage-drop-compensated active balancing, respectively — that underpin subsequent industry approaches.

Sungrow Power Supply addresses the ESS-specific challenge of capacity correction across multiple modules operating under partial-cycle conditions, targeting module-level SOC consistency rather than cell-level balancing.

The Shift to Statistical and Model-Based Detection

An important trend visible across filings from 2022 onward is the shift from threshold-based balancing triggers to statistical and model-based anomaly detection. Moving windows, deviation rankings, cumulative deviation tracking, and machine learning-assisted state prediction all appear as next-generation diagnostic tools. LG Energy Solution’s 2025 battery inspection apparatus applies machine learning to battery status data to generate predictive state assessments — a significant departure from the fixed-threshold approaches that characterised earlier filings. This transition reflects a broader industry recognition, aligned with roadmaps from organisations including WIPO, that AI-driven predictive maintenance is becoming central to battery system management as pack sizes and cell counts increase. The PatSnap IP intelligence platform tracks this trend across the full global patent corpus, enabling R&D teams to monitor the competitive frontier in real time.

“The shift from threshold-based balancing triggers to statistical and model-based anomaly detection — visible across filings from 2022 onward — reflects the industry’s recognition that fixed thresholds cannot adapt to pack aging without recalibration.”

The PatSnap R&D intelligence platform enables battery engineers and BMS architects to track these emerging methodologies across the full global patent corpus, identify white-space opportunities, and benchmark their own IP positions against the assignees profiled in this analysis.