Knowledge base
BMS (battery protection)
Possible causes
- Cell voltage outside protection limits
- Over-current or short-circuit protection
- Temperature outside the permitted range
- BMS or communication fault
Safe test steps
- Pack temperature (let it rest at room temperature, repeat).
- Manufacturer wake/reset (e.g. connect the original charger) per instructions.
- Cell-group voltages – trained technicians with insulated tools only.
Workshop reference values
- Balanced pack at rest: group spread typically ≤ 30 mV (workshop rule of thumb).
Repair approach
- Remove the cause (temperature, charge), then manufacturer reset.
- BMS replacement/repair only at a battery specialist.
Tools needed
- Digital multimeter (CAT III, fused inputs)
- Manufacturer dealer diagnostic tool/software (if available)
Safety
- Never bypass the BMS or revive deeply discharged cells with a normal charger.
Related verified fault codes
| Code | Meaning | Component | Reliability |
|---|---|---|---|
| Bafang 22 | BMS communication fault | BMS (battery protection) | Per manufacturer documentation |
| Bafang 44 | Single cell voltage too high | BMS (battery protection) | Per manufacturer documentation |
| Bafang 47 | Battery SOC too high | BMS (battery protection) | Per manufacturer documentation |
| Bafang 48 | Battery SOC too low | BMS (battery protection) | Per manufacturer documentation |
| Xiaomi 21 | Battery (BMS) communication fault | BMS (battery protection) | Widely published – may differ by model/firmware |
| Xiaomi 22 | BMS password/authentication error | BMS (battery protection) | Widely published – may differ by model/firmware |
| Xiaomi 23 | BMS serial number error (default value) | BMS (battery protection) | Widely published – may differ by model/firmware |
| Segway-Ninebot 21 | Battery (BMS) communication fault | BMS (battery protection) | Widely published – may differ by model/firmware |
| Segway-Ninebot 22 | BMS password/authentication error | BMS (battery protection) | Widely published – may differ by model/firmware |
| Segway-Ninebot 23 | BMS serial number error (default value) | BMS (battery protection) | Widely published – may differ by model/firmware |