Lithium Battery Diagnostic Process

Created by Scott Chen, Modified on Wed, 15 Oct at 11:48 AM by Scott Chen

Purpose: To standardize diagnostic testing and root cause classification for lithium battery packs. This SOP applies to LiFePO₄ and related lithium chemistries for both field and RMA inspections.

Procedure Steps:

Step	Description	Expected Observation	Action / Interpretation
1. Visual Inspection	Check for swelling, leaks, cracks, or burn marks.	• Swelling or leakage → unsafe • Clean, intact casing → proceed	If swelling or leakage found, stop testing and scrap the unit.
2. Voltage Test (Multimeter)	Measure total pack voltage at terminals.	• 0V = BMS cutoff or fuse open • <10V = deep discharge • 12.8–13.4V = normal	If <10V, classify as improper maintenance; if 0V, check for BMS protection.
3. Wake-Up / Charge Test	Connect to correct LiFePO₄ charger and observe response.	• No current = BMS lock • Short charge then stop = imbalance	If no charge flow, attempt low-current wake-up (<1A). Record recovery behavior.
4. Load Test	Discharge at ~0.2C rate (e.g., 20A for 100Ah pack).	• Voltage drop fast = high internal resistance • Stable = good pack	If collapse observed, suspect aging or deep-discharge neglect.
5. BMS / Cell Analysis	Read BMS via Bluetooth if available; otherwise, probe balance leads.	• One cell <2.0V = neglect • Balanced cells but no output = BMS fault	Record cell readings; identify low or unresponsive cell for defect classification.
6. Charge Retention Test	Charge briefly, disconnect, wait 1 hr, remeasure voltage.	• Drop >0.5V → internal leakage (neglect) • Stable voltage → normal	Voltage rebound loss confirms degradation from delayed charging.
7. Final Diagnosis	Summarize findings and classify issue.	See result criteria below.	Proceed to classification table.

Result Classification Table:

Condition	Likely Cause	Classification	Warranty Status
Pack 0–9V, long idle period	Delayed charging / storage neglect	Improper maintenance	Non-warranty
1–2 cells <2.0V, others normal	Storage imbalance	Improper maintenance	Non-warranty
All cells healthy but no output	BMS MOSFET or fuse failure	Defective BMS	Warranty
Cells balanced but 1 drops fast under load	High internal resistance	Defective cell	Warranty
Swelling, burns, melted terminals	Short circuit / user damage	User damage	Non-warranty

Conclusion: If the pack shows low voltage, locked BMS, and no physical damage, the issue is classified as improper maintenance (non-warranty). If normal voltage but functional failure, classify as a defective BMS or cell (warranty). All physical damage cases are non-warranty.