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Battery and BMS
Most e-bike faults involve the battery and the BMS. Here you find safe measurement steps, workshop reference values and the related verified fault codes.
Voltage of a fully charged Li-ion pack
| System | Cells (S) | Nominal | Fully charged |
|---|---|---|---|
| 24 V | 7S | 25.2 V | 29.4 V |
| 36 V | 10S | 36.0 V | 42.0 V |
| 48 V | 13S | 46.8 V | 54.6 V |
| 52 V | 14S | 50.4 V | 58.8 V |
Calculation: S × 3.6 V nominal, S × 4.20 V fully charged (Li-ion). The exact limit comes from the cell datasheet.
Battery
Possible causes
- Aged cells, increased internal resistance
- Weak or discharged cell group
- Contact fault at battery connector/mount
- BMS protection or BMS fault
Safe test steps
- Resting voltage at the pack output vs. the nominal class (S × 3.6 V nominal, S × 4.20 V full for Li-ion).
- Load test with current: R = ΔU / I (E-Bike Doctor battery calculator).
- Condition of mount contacts, discoloration, play.
Workshop reference values
- Li-ion cell: 3.6–3.7 V nominal, 4.20 V full; manufacturer minimum typically 2.5–3.0 V (per datasheet).
- Pack full voltage (Li-ion): 7S 29.4 V · 10S 42.0 V · 13S 54.6 V · 14S 58.8 V.
Repair approach
- Full charge with the original charger, then re-measure.
- Pack repair/re-celling only by a qualified battery shop with identical matched cells; otherwise replace the pack.
Tools needed
- Digital multimeter (CAT III, fused inputs)
- Fused load tester or clamp meter
- Manufacturer dealer diagnostic tool/software (if available)
Safety
- Do not charge or open a swollen, hot, damaged, hissing or smelling pack – isolate it safely.
- Never connect an ammeter directly across the battery. Never bypass the BMS.
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.
Charger
Possible causes
- Faulty charger or charger cable
- Damaged/corroded charging socket
- BMS charge protection (temperature, cell voltage)
Safe test steps
- Charger open-circuit output vs. its label value.
- Does pack voltage rise while charging (measure after 5–10 min)?
- Charging socket contacts, polarity, mechanical damage.
Workshop reference values
- Li-ion charger final voltage: S × 4.20 V (e.g. 10S → 42.0 V); tolerance typically ±1 %.
- Charging temperature: most Li-ion cells must not be charged below 0 °C (per datasheet).
Repair approach
- Replace the charger with an approved one of the same voltage.
- Replace the charging socket/cable.
Tools needed
- Digital multimeter (CAT III, fused inputs)
- Basic hand tools, insulated screwdrivers
Safety
- Do not charge unattended, near flammables, or a damaged/hot pack.
Voltage
Possible causes
- Low state of charge / heavy sag under load
- Over-voltage (wrong charger, unsuitable battery)
- Faulty voltage sensing in the controller
Safe test steps
- Pack voltage at rest and under load vs. the controller voltage class.
- Charger output voltage per label (S × 4.20 V Li-ion).
Workshop reference values
- Typical controller low-voltage cutoff: approx. 3.0–3.15 V/cell (~30–31.5 V on 36 V) – controller-specific.
Repair approach
- Charge the battery; if it still drops under load: battery diagnosis.
- Replace a battery/charger of the wrong voltage with a matching one.
Tools needed
- Digital multimeter (CAT III, fused inputs)
- Fused load tester
Safety
- Never use a battery or charger of a different voltage with the system.
Related verified fault codes
| Code | Meaning | Component | Reliability |
|---|---|---|---|
| Bosch 530 | Battery fault | Battery | Per manufacturer documentation |
| Bosch 602 | Internal battery fault during charging | Battery | Per manufacturer documentation |
| Bosch 603 | Internal battery fault | Battery | Per manufacturer documentation |
| Bosch 606 | External battery fault | Battery | Per manufacturer documentation |
| Bosch 610 | Battery voltage fault | Voltage | Per manufacturer documentation |
| Bosch 620 | Charger fault | Charger | Per manufacturer documentation |
| Bosch 640 | Internal battery fault | Battery | Per manufacturer documentation |
| Bosch 655 | Multiple battery fault | Battery | Per manufacturer documentation |
| Shimano STEPS E021 | Connected battery conforms to the standard but is not supported | Battery | Per manufacturer documentation |
| Shimano STEPS E022 | Connected battery does not conform to system standards | Battery | Per manufacturer documentation |
| Bafang 07 | Over-voltage protection | Voltage | Per manufacturer documentation |
| Bafang 22 | BMS communication fault | BMS (battery protection) | Per manufacturer documentation |
| Bafang 41 | Total battery voltage too high | Voltage | Per manufacturer documentation |
| Bafang 42 | Total battery voltage too low | Voltage | Per manufacturer documentation |
| Bafang 43 | Total power from battery cells too high | Battery | 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 |
| Xiaomi 24 | Supply voltage abnormal | Voltage | 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 |
| Segway-Ninebot 24 | Supply voltage abnormal | Voltage | Widely published – may differ by model/firmware |
Calculate it in the app
The battery calculator of the Android and Windows apps computes cell groups, state of charge, range and voltage sag for 7S–14S packs – every formula can be checked.