When the range of your electric vehicle frequently drops and it struggles to climb hills, replacing the battery becomes an inevitable choice. However, random replacement may lead to power imbalance and even violate regulations. This article combines industry standards and technical principles to distill the "1 Core 3 Rules" to help you replace batteries scientifically, balancing performance and safety.
I. Core Principle of Battery Replacement: "Parameter Matching Takes Precedence over Capacity Stacking"
The battery, motor, and controller of an electric vehicle form a closed-loop system. When replacing the battery, the principle of "consistent voltage, compatible current, and protocol matching" must be followed:
Voltage matching is the bottom line: The rated voltage of the battery must be consistent with the nominal voltage of the original vehicle's motor and controller (for example, for a 60V system in the original vehicle, it is strictly forbidden to replace it with a 72V battery). A voltage that is too high will burn out the motor coils or the controller MOSFETs, while a voltage that is too low will result in insufficient power output.
Current compatibility is key: The maximum discharge current of the new battery (unit: C) must be ≥ the peak current of the original vehicle's motor. For instance, the peak current of a 500W motor is approximately 25A. If a 20Ah lithium battery is chosen, its discharge rate must be ≥ 1.25C (i.e., 25A/20Ah = 1.25C) to avoid a sudden drop in voltage during high current discharge.
BMS protocol adaptation: For smart electric vehicles, it is essential to ensure that the BMS (Battery Management System) of the new battery is compatible with the vehicle's main control protocol; otherwise, problems such as abnormal charging and incorrect range display may occur.
Ⅱ.Three Golden Rules for Battery Replacement: Compliant Operations Extend the Battery's "Second Spring"
Rule 1: Type Selection "Lithium Batteries as the Main Option, Lead-Acid as a Secondary Choice"
Priority should be given to lithium batteries:
✅ High energy density (twice to three times the capacity of lead-acid batteries of the same volume), suitable for users seeking range upgrades
✅ Supports fast charging (can reach 80% in 30 minutes), reducing waiting time
✅ Light weight (about 1/3 of lead-acid batteries), improving vehicle handling
⚠️ Note: Confirm whether the vehicle frame supports lithium battery installation (some models are only compatible with lead-acid battery compartments)
Applicable scenarios for lead-acid batteries:
✅ Limited budget (cost is about half of lithium batteries)
✅ Frequent battery removal (e.g., in high-rise buildings without elevators), lead-acid structure is more vibration-resistant
✅ Low-temperature environments (-10°C and below, lead-acid batteries have a slower capacity decline than low-end lithium batteries)
Rule 2: Capacity Upgrade "Follow the Original Vehicle's Design Limit"
Formula to calculate the safety threshold:
New battery capacity (Ah) ≤ Original vehicle controller current limit (A) × Motor efficiency coefficient (0.8 - 0.9)
Example: If the controller current limit is 30A and the motor efficiency is 0.85, then the maximum suitable capacity ≈ 30A × 0.85 ≈ 25.5Ah, and a 24-25Ah battery can be selected.
Warning of illegal risks:
❌ Exceeding the capacity limit may lead to:
① Insufficient battery compartment cooling causing thermal runaway
② False range indication (fixed motor power, large-capacity batteries cannot be fully discharged)
③ Violation of the "Safety Technical Specifications for Electric Bicycles" (GB17761), affecting vehicle annual inspection
Rule 3: Installation and Activation "Standardized Process"
1. Power-off operation: Disconnect the vehicle's main power supply first to avoid short circuits between the positive and negative terminals.
2. Interface inspection: Clean the electrode interfaces, apply vaseline to prevent oxidation, and ensure a firm connection.
3. Initial charging:
Lead-acid battery: The first charge should last 8-10 hours to activate the active substances on the plates.
Lithium battery: Charge to 90% for the first time, avoiding overcharging (batteries with BMS can be used directly).
4. Data calibration: Ride for 3-5 kilometers after replacement to allow the vehicle's MCU to learn the new battery's voltage curve and avoid range display deviations.
Ⅲ.Pitfall Avoidance Guide: Three Maintenance Tasks to Do After Battery Replacement
1. Regular balanced charging:
Lead-acid battery: Perform a 2-hour extended charge once a month to balance the voltage of each individual battery.
Lithium battery: Conduct a "full charge and discharge" (charge to 100% and then ride until 20% remaining) every three months.
2. Temperature management:
Summer: Avoid direct sunlight (battery temperature > 45°C, charging efficiency drops by 30%).
Winter: Preheat the battery before charging (wrap it in a cotton blanket to enhance activity).
3. Dynamic monitoring:
Install a battery monitoring app (such as NIU Electric or Yadea Smart Manager) to view the number of charge and discharge cycles and battery health in real time. - Every six months, go to the store to test the battery's internal resistance. (Replace the battery if the internal resistance increase is more than 30%)
Ⅳ.Legal reminder: These modification behaviors are illegal.
- Do not increase the voltage without authorization: For example, modifying a 48V system to a 60V battery is an illegal act of "altering the vehicle structure and parameters".
- Lithium batteries must pass 3C certification: The risk of self-ignition of inferior lithium batteries is 5 to 8 times that of regular products, and insurance companies may refuse to compensate.
- Keep the original battery code: After replacement, the new battery serial number must be registered in the "Battery Information" column of the driving license to avoid suspicion of license plate fraud.
Conclusion
Replacing the battery of an electric vehicle is not merely a simple "trade-in for a new one", but rather a re-balancing of the system's performance. Adhering to the logic of "parameter matching as the core, type, capacity, and process as the rules" can not only prevent safety hazards but also maximize the performance of the new battery. Remember: a compliant upgrade is the correct path to extend the vehicle's life cycle. Blindly pursuing a large capacity will only be counterproductive. With good usage habits after battery replacement (such as avoiding sudden acceleration and regular maintenance), a 30% increase in range is not difficult to achieve.