I. Core Principles and Advantages of Parallel Batteries
Parallel batteries connect multiple batteries by linking their positive terminals together and negative terminals together, forming a battery network with the same voltage but significantly increased capacity and current output capability. The core advantages include:
- Capacity Expansion: Total capacity equals the sum of individual battery capacities. For example, four 2000mAh batteries in parallel provide a total capacity of 8000mAh, extending device runtime.
- Current Enhancement: Total current output capability is the sum of individual battery currents. In applications like electric motors and power tools, parallel connections meet high-power demands.
- Redundancy Design: If one battery fails, others continue to supply power, enhancing system reliability. For example, solar street lights can maintain illumination even if one battery fails.
II. Application Scenarios and Typical Cases
1. Low Voltage, High Current Requirements
Elderly Mobility Scooters: Use parallel 48V/200Ah lead-acid batteries to meet continuous power needs for low-speed travel.
Portable Audio Systems: Parallel 18650 lithium batteries enable extended high-volume playback.
2. Energy Storage Systems
Solar Street Lights: Parallel LiFePO4 battery arrays store daytime energy for nighttime use; single battery failure doesn't affect overall operation.
Home Energy Storage: Tesla Powerwall uses parallel battery modules to achieve 13.5kWh capacity, meeting household emergency power needs.
3. Industrial Equipment
Forklifts: Parallel lead-acid battery arrays provide high current output to drive hydraulic systems.
Data Center UPS: Parallel lithium battery arrays ensure continuous power during outages, maintaining server operation.
III. Installation and Usage Specifications
1. Battery Selection
Parameter Consistency: Use batteries of the same model, capacity, and batch. For example, when paralleling four 12V100Ah lead-acid batteries, ensure internal resistance difference ≤5mΩ and voltage difference ≤0.1V.
Condition Check: Test battery voltage and internal resistance before installation; exclude batteries with leaks or bulging.
2. Connection Techniques
Wire Specifications: Select wire cross-section based on total current. For example, with four 200Ah batteries in parallel, maximum discharge current can reach 800A, requiring 95mm² copper wire.
Connection Method: "Series first then parallel" reduces management complexity. For example, BYD K9 buses parallel three 200Ah/540V battery systems to form a 324kWh/600Ah energy storage system.
3. Safety Protection
Insulation Treatment: Wrap connection points with insulation tape to prevent short circuits.
Ventilation Design: Install battery arrays in well-ventilated areas to avoid heat accumulation. For example, data center UPS battery rooms require air conditioning systems to maintain temperature at 25±2°C.
IV. Management and Maintenance Key Points
1. Balance Control
- Passive Balancing: Uses parallel resistors to consume charge from higher voltage batteries, but with lower efficiency.
- Active Balancing: Uses DC-DC converters to transfer energy between batteries, achieving efficiency over 95%. For example, CATL standard enclosures support two parallel branch enclosures equipped with active balancing modules.
2. Status Monitoring
- Voltage Detection: Regularly measure individual battery voltages; adjust if differences exceed 5%.
- Temperature Monitoring: Activate cooling systems if battery surface temperature exceeds 50°C.
3. Charging Management
- Constant Current/Constant Voltage Charging: First charge with 0.3C current to cutoff voltage (e.g., 14.4V), then switch to constant voltage until current drops to 0.05C.
- Avoid Overcharging: Set charging cutoff voltage error ≤0.5% to prevent lithium plating.
V. Common Issues and Solutions
1. Uneven Current Distribution
Cause: Differences in battery internal resistance. For example, batteries with 10% internal resistance difference can have up to 20% current distribution variation.
Solution: Use internal resistance matching technology; select batteries with internal resistance differences ≤3%.
2. Thermal Runaway Risk
Case: A data center UPS experienced a fire due to loose battery connections increasing contact resistance, raising local temperature to 120°C.
Prevention: Regularly check connection tightness; use infrared thermometers to monitor temperature.
3. Life Degradation
Data: Parallel battery arrays have 10%-20% shorter cycle life than single batteries due to accelerated aging from imbalanced charging/discharging.
Optimization: Use Battery Management Systems (BMS) for balance control, extending life to over 8 years.
VI. Future Trends: Intelligent Parallel Battery Systems
With advancements in battery technology, intelligent parallel systems are becoming mainstream:
- Wireless BMS: Real-time battery status monitoring via Bluetooth or Wi-Fi reduces wiring complexity.
- Adaptive Balancing: Dynamically adjusts balancing strategies based on battery status, improving efficiency.
- Cloud Management: Uploads battery data to the cloud for remote diagnostics and maintenance. For example, Tesla Powerwall analyzes user electricity habits via cloud to optimize charging strategies.