Lithium-ion batteries power applications ranging from electric mobility to industrial backup systems. Despite their reliability, several failure modes frequently appear across different lithium chemistries such as NMC, LFP, NCA, and LMO.
Each failure has its own mechanism, detection method, and mitigation strategy.
This article summarizes five common, engineering-verified failure scenarios, together with real-world test insights and practical diagnostics.

For readers looking for deeper BMS fundamentals, see our guide:What is a Battery Management System (BMS)?

1. Cell Imbalance (Voltage Drift Between Cells)

What Happens

Cells in a series pack gradually drift apart due to differences in:

• Internal resistance

• Capacity degradation

• Temperature exposure

• Manufacturing tolerances

When one cell reaches full/empty earlier than others, the BMS must prematurely stop charging or discharging—reducing usable capacity.

Engineering Symptoms

• Voltage deviation > 30–50 mV (mild imbalance)

• 100 mV (critical imbalance, high risk during charging)

• SOC estimation becomes unstable

• Pack prematurely terminates charge

Why It Occurs

• High discharge loads

• Repeated fast charging

• Using mixed-batch or different-aging cells

• Poor thermal management causing uneven heating

Correct Technical Solutions

✔ 1. Active/Passive Balancing

• Passive balancing removes excess charge through bleed resistors.

• Active balancing transfers energy from high-voltage to low-voltage cells.
  Bench test data shows active balancing reduces drift 3–5× faster in large packs.

✔ 2. Thermal Equalization

Cell drift strongly correlates with heat differences. Keeping ΔT < 3°C significantly reduces imbalance.

✔ 3. Diagnostic Procedure (Verified Method)

1. Fully charge pack to manufacturer spec

2. Rest 60 minutes for voltage stabilization

3. Record cell voltages and temperature

4. Discharge at 0.5C and capture divergence trend

5. Identify “weak” cells based on IR rise and voltage sag

2. Overheating & Thermal Accumulation

What Happens

Lithium cells generate heat during:

• High current charging/discharging

• Internal short circuits

• MOSFET conduction losses in the BMS

• Ambient exposure above 45°C

Uncontrolled heat accelerates SEI breakdown and gas formation.

Common Warning Signs

• Temperature > 60°C under 0.5–1C load

• Sudden swelling (common in polymer lithium packs)

• MOSFET temperature rising faster than cell temperature

• Hotspots detected by IR camera

Test Insight (Empirical Data)

In controlled lab tests (KURUI reliability lab):

• Cell temperature rose 18–22°C during continuous 15A discharge on compact packs

• With no heat dissipation, MOSFETs reached 74°C even under rated load

Correct Technical Solutions

✔ Heat Spreaders/Graphite Pads

Equalizes surface temperature, lowering ΔT by up to 8°C.

✔ MOSFET Upgrading

Lower Rds(on) MOSFETs reduce conduction loss by 12–30%.

✔ Multi-NTC Temperature Monitoring

Industrial BMS uses 2–4 NTCs to detect hotspots instead of relying on a single point.

✔ Thermal Shutdown Logic

Config example (varies by BMS model):

• Charge stop: 55°C

• Discharge stop: 65°C

• Hard cutoff: 70°C

3. Capacity Loss & Accelerated Aging

What Happens

Lithium packs lose capacity over cycles due to:

• SEI layer growth

• Lithium plating

• High-temperature exposure

• Over-discharge events

Typical degradation rate:

• LFP: 1–2% per 100 cycles

• NMC/NCA: 2–4% per 100 cycles

Why It Occurs

• Storing packs above 80% SOC at high temperature

• Repeated deep discharging to the UV threshold

• Fast charging beyond the manufacturer’s limit

Correct Solutions

✔ Gentle Charge Strategy

Charge to 80–90% SOC when longevity > range.
Tests show a 2× cycle-life increase when limiting charge voltage.

✔ Avoid Deep UV Events

Voltage < 2.5V may cause copper dissolution + internal micro-short.

✔ Store at 30–50% SOC

Minimizes SEI growth.

✔ Periodic Capacity Recalibration

Perform a full charge/discharge every 80–100 cycles to correct SOC drift.

4. Internal Short Circuits (ISC) & Manufacturing Defects

What Happens

Internal shorts are typically caused by:

• Metallic contaminants

• Separator damage

• Mechanical compression

• Lithium dendrite penetration (common in cold fast charging)

ISC may remain latent until temperature triggers runaway.

Real Diagnostic Indicators

• Rapid self-discharge (drop >50 mV/day)

• Temperature rise during rest

• Abnormal voltage sag under low load

• IR increase >30% compared to pack average

Correct Technical Solutions

✔ Pack Quarantine & Full Diagnostic

Cells suspected of ISC must be isolated and tested independently.

✔ X-ray / CT Non-Destructive Testing (For OEM scale)

Used in large factories to identify structural defects.

✔ BMS Fast-Trip Short-Circuit Protection

Modern BMS chips cut load within 200–600 μs during a hard short.

5. BMS Failure or Incorrect Parameter Configuration

Symptoms

• No charge/no discharge

• SOC jumps

• Balancing not functioning

• False OVP/UVP triggers

• Communication interruptions

Root Causes

• Incorrect OVP/UVP thresholds for the chemistry

• MOSFET degradation

• Firmware bugs

• Shunt resistor calibration drift

• Poor grounding layout

Correct Solutions

✔ Parameter Validation

Example recommended safe limits (chemistry-dependent):

✔ MOSFET Thermal Derating

Ensure MOSFET operates within SOA curve.

✔ Communication Integrity Testing

CAN/UART error rate must < 0.1% under EMI load.

✔ Grounding & PCB Layout Review

Prevent sampling noise that leads to OVP/UVP misjudgment.

Real-World Case Study

Case: Electric Scooter Pack Premature Shutdown Problem

Pack Specs:

• 10S4P NMC

• 20A continuous

• Off-the-shelf BMS

Observed Problems:

• Sudden cut-off on inclines

• 130–180 mV cell drift

• Surface temperature hit 63°C

KURUI Engineering Intervention:

1. Added dual NTC sensors

2. Upgraded MOSFETs to lower Rds(on)

3. Added active balancing module

4. Re-calibrated shunt for accurate current measurement

Result after 60-cycle validation:

• Temperature reduced 12°C

• Drift reduced to <25 mV

• No cut-off events after modifications

Conclusion

Lithium battery failures are avoidable when using proper engineering methods, accurate diagnostics, and a reliable BMS ecosystem.
For complex issues, pack builders should rely on:

• Chemistry-correct parameters

• Verified balancing strategies

• Real-world thermal testing

• Hardware safety redundancy

• Firmware with validated logic

KURUI provides engineering-backed BMS solutions for lithium battery systems used in industrial, consumer, and mobility applications, supporting OEM customization and project-level technical verification.

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