BYD BYD Battery Management System Error Code BY011

BYD Battery Major Voltage

Model: BYD Battery Management System | Code: BY011

Applicable Systems

BYD Battery Management System

Symptoms

The battery cell voltage has dropped below 2.8V per cell, indicating over-discharge. The BMS disconnects the battery to prevent cell damage.

Continuous load on the battery after the BMS requested a shutdown
Self-discharge over an extended storage period without maintenance charge
BMS balancing circuit failed, allowing one cell to discharge below the safe threshold
Parasitic drain from connected equipment after the main contactor opened

Step 1: Measure each cell voltage with a multimeter and identify the low cells
Cells below 2.5V require careful recovery charging; below 2.0V may be permanently damaged
Step 2: Apply a low-current recovery charge (0.05C) to the low cells individually
Monitor temperature; if any cell exceeds 45C, stop and replace the cell
Step 3: Verify the BMS balancing circuit operates during charging
If the balancing circuit is not functioning, the BMS needs service
Step 4: After recovery, perform a full charge cycle and verify all cells balance above 3.0V
If cells do not balance, replace the weak cells or the entire battery pack

Reset: The BMS reconnects the battery automatically once all cells are above the minimum threshold during charging.

Q: What is the minimum safe cell voltage?
For LiFePO4: 2.5V. For NMC: 2.8V. Discharging below these levels causes irreversible chemical damage.
Q: How do I recover an over-discharged cell?
Apply 0.05C (5% of rated capacity) constant current until voltage reaches 3.0V, then switch to normal CC-CV charging.
Q: How long can I store a lithium battery?
At 40-50% state of charge in a cool, dry place: 6-12 months. Check voltage every 3 months and top up if below 3.0V per cell.