In the battery industry, "common‑port" and "separate‑port" are two common interface design approaches. Unlike the common‑port design, where charging and discharging share the same interface, the separate‑port design completely separates the charging and discharging ports, making them independent. This seemingly simple physical separation involves systematic differences in circuit design, BMS management, thermal management, and testing methods.
Q&A: Quick understanding of battery separate‑port charge/discharge
Q1: What is battery separate‑port charge/discharge?
The charging port and discharging port are independent. A battery pack typically has three terminals (charge positive, discharge positive, and common negative). Common‑port designs use only two wires.
Q2: What are the key advantages of separate‑port design?
It allows independent control of charge and discharge paths, enabling MOSFET selection tailored to different current levels. In high‑discharge, low‑charge scenarios, this reduces cost, lowers internal resistance, minimizes heat generation, and supports simultaneous charging and discharging.
Q3: What are the main differences between common‑port and separate‑port designs?
| Aspect | Common‑port | Separate‑port |
| Wiring | 2 wires | 3 wires |
| Path | Shared | Fully independent |
| MOSFETs | Series‑connected, identical specs required | Independent selection possible |
| Cost / resistance | Higher | Lower |
| Best suited for | Similar currents | Discharge >> charge |
| Simultaneous use | Not supported | Supported |
Table 1 common vs separate port charge/discharge
Q4: Which batteries use separate‑port design?
AGV/AMR robot batteries, electric forklifts, high‑rate energy storage systems, and some power tools – all characterized by discharge current far exceeding charge current.
Q5: How to test separate‑port batteries?
Charge and discharge tests must be performed separately: charge port tests verify overcharge protection and charging efficiency; discharge port tests verify over‑discharge protection and discharge capacity. Test equipment must support separate‑port wiring, such as NEWARE's CE‑6000 series with "‑B" suffix models.
Q6: What precautions should be taken during charging?
The charge port provides only overcharge protection – it does not provide discharge protection. Also, the charge port typically has a lower current capability, so high‑rate discharging through the charge port is not recommended. When parallel‑charging multiple packs, each pack should use its own charger.
Current battery market: High‑rate applications drive interface design differentiation
The global lithium‑ion battery market is in an unprecedented period of expansion. In 2026, total global demand is expected to reach approximately 2,629 GWh, a year‑on‑year increase of 28%, with power battery demand at about 1,678 GWh and energy storage battery demand at about 795 GWh. As industrial applications such as AGV/AMR robots, electric forklifts, and high‑rate energy storage systems expand rapidly, the need for differentiated interface designs in battery systems is growing.
In the field of industrial mobile robots, batteries often face a typical operating condition where the discharge rate is much higher than the charge rate. Taking an AGV battery as an example: suppose the discharge rate is 10C and the charge rate is only 1C, the corresponding maximum continuous discharge current is 20A, while the maximum continuous charge current is only 2A. With a common‑port design, the discharge current must pass through the charge‑control MOSFET, forcing the charge MOSFET to have the same current‑carrying capacity as the discharge MOSFET, leading to higher cost, higher internal resistance, and increased heat generation.
Based on this real‑world need, separate‑port charge/discharge design has gained wide adoption in high‑rate discharge scenarios. Brands such as HAWKER and SAPHIR already feature separate‑port charging and discharging as standard in their AGV lithium battery products. In these batteries, the charge and discharge ports are fully isolated. The normal charging voltage at the charge port is 29.2V (for 24V systems), supporting fast charging (e.g., 2C fast charging, fully charged in half an hour), while the discharge port offers greater continuous discharge capability (e.g., 2C continuous, 3C instantaneous).
Figure 1 industrial mobile robots
What is battery separate‑port charge/discharge?
Definition
Battery separate‑port charge/discharge refers to an interface design where the charging input and discharging output are independent and not shared. In this design, the battery pack typically has three external terminals: charge positive (P+), discharge positive (P−), and common negative (C−). Alternatively, the charge positive and discharge positive may be shared while the negative terminals are separated.
From the protection board (BMS) architecture perspective, separate‑port design means that the charge MOSFET and discharge MOSFET control their respective circuits independently. The charge port provides overcharge protection only for the charging circuit; the discharge port provides over‑discharge protection only for the discharging circuit. This "separate‑control" architecture is fundamentally different from the "common‑control" architecture of common‑port designs, where charge and discharge MOSFETs are connected in series.
Core differences between common‑port and separate‑port
Common‑port design uses a single interface for both charging and discharging, with only two wires (positive and negative) on the battery pack. In this design, the charge and discharge MOSFETs are connected in series, so the discharge current must pass through both the charge‑control MOSFET and the discharge‑control MOSFET.
Separate‑port design, on the other hand, completely separates the charge and discharge paths. The battery pack has three wires – charge positive, discharge positive, and common negative. Charging and discharging are controlled by independent MOSFETs without interference.
This physical separation provides several key advantages:
Cost optimization: Since discharge current is usually much higher than charge current, separate‑port design allows the discharge path to use high‑current, low‑resistance MOSFETs, while the charge path can use lower‑current, more cost‑effective MOSFETs, achieving on‑demand configuration.
Reduced internal resistance: The discharge path no longer passes through the charge MOSFET, resulting in a shorter path, lower internal resistance, and less heat generation.
Functional independence: Supports simultaneous charging and discharging without interference. The charge port handles only charging, and the discharge port handles only discharging, each managed independently.
Enhanced safety: Two independent circuits control charging and discharging. The discharge port is not live during charging, and the charge port is not live during discharging, effectively improving the safety of lithium batteries during use.
What is the purpose of separate‑port charge/discharge design?
In power batteries and industrial robot battery applications, discharge rates much higher than charge rates are common. Taking an AGV battery, the discharge rate can reach 10C while the charge rate is typically only 1C. With a common‑port design, the discharge current must pass through the charge‑control MOSFET, forcing the charge MOSFET to also have the same high‑current capacity, leading to unnecessary cost increases.
Separate‑port design separates the charge and discharge paths, allowing independent selection – high‑current MOSFETs for the discharge path to meet high‑rate discharge demands, and low‑current MOSFETs for the charge path to control costs. This "on‑demand configuration" philosophy offers significant cost advantages in high‑rate discharge scenarios.
Optimizing energy conversion efficiency and system reliability
Separating the charging and discharging circuits allows independent optimization of energy conversion efficiency for each, improving overall system efficiency. At the same time, separate‑port design can enhance device reliability and flexibility.
In terms of safety, using two independent circuits to control charging and discharging means the discharge port is not live during charging and the charge port is not live during discharging, effectively preventing cascading risks from a single circuit failure. Some separate‑port batteries also include a discharge diode in series with the discharge port, with its conduction direction matching the current flow during discharge, further enhancing circuit safety.
Supporting simultaneous charging and discharging
Another important advantage of separate‑port design is that it supports simultaneous charging and discharging without interference. In industrial scenarios such as AGV/AMR that require continuous operation, the battery can be charged while continuing to power the equipment, without interrupting operation. This "uninterrupted operation" capability is significant for improving equipment utilization and production efficiency.
Fool‑proof design and interface standardization
Some separate‑port batteries use different plug specifications to distinguish the charge port from the discharge port, effectively preventing user misconnection. This fool‑proof design is especially important in industrial environments, significantly reducing equipment failures and safety accidents caused by wiring errors.
Which battery specifications use separate‑port charge/discharge design?
Separate‑port charge/discharge design is not applicable to all battery types; its use is concentrated in scenarios where the charge and discharge currents differ significantly.
AGV/AMR robot batteries
This is the most common application area for separate‑port design. Products such as HAWKER EV series LFP batteries and SAPHIR EV series lithium batteries feature separate‑port charge/discharge. Typical specifications include 24V/48V/72V/96V voltage platforms, capacities from 30Ah to 200Ah, supporting 1C‑2C charging and 2C‑3C discharging. The charge and discharge ports in these batteries are fully isolated, enabling simultaneous operation.
Electric forklifts and industrial vehicle batteries
Industrial vehicles also face high‑discharge, low‑charge conditions, so separate‑port design is also widely used in electric forklifts, tow tractors, and similar equipment.
High‑rate energy storage systems
Some energy storage systems also set the charging and discharging terminals independently to improve charge/discharge efficiency. This design offers advantages in fast‑response frequency‑regulation storage applications.
Power tools and special equipment batteries
Separate‑port design also sees some use in high‑power power tools, emergency power supplies, and similar devices.
How to identify separate‑port batteries
The simplest way to identify whether a battery uses separate‑port design is to check the number of terminals: common‑port batteries typically have only 2 terminals (positive and negative), while separate‑port batteries usually have 3 or more terminals (charge positive, discharge positive, common negative). In addition, product specification sheets usually explicitly state "separate charge/discharge ports".
How to test separate‑port charge/discharge batteries
Testing separate‑port batteries differs significantly from testing common‑port batteries. The key difference is that charge and discharge tests must be performed independently on their respective ports.
Pre‑test preparation
Sample confirmation: First confirm the battery's interface type – check the battery label or specification sheet to determine whether it is separate‑port design, and identify the pin definitions of the charge and discharge ports.
Equipment selection: Choose a battery charge‑discharge test system that supports separate‑port wiring. The test equipment must have independent charge and discharge control capabilities, allowing separate connection to the charge and discharge ports. NEWARE's CE‑6000 series with "‑B" suffix models support separate‑port charge/discharge wiring. The equipment should include reverse‑connection protection and power‑loss data protection.
Wiring confirmation: Separate‑port batteries have three terminals – charge positive, discharge positive, and common negative. During testing, ensure that charge tests are connected to the charge port, discharge tests to the discharge port, and the common negative is shared.
Charge performance testing
Overcharge protection test: Charge the battery through the charge port to verify that the BMS can promptly disconnect the charging circuit when the battery reaches the overcharge protection voltage.
Charging efficiency test: Record the voltage and current curves during charging, calculate charging efficiency, and verify whether the design targets are met (e.g., normal charging voltage for a 24V iron‑phosphate battery is 29.2V).
Charge rate test: Verify the battery's charge acceptance and temperature rise performance at different charge rates (e.g., 0.5C, 1C, 2C).
Discharge performance testing
Over‑discharge protection test: Discharge the battery through the discharge port to verify that the BMS can promptly disconnect the discharge circuit when the battery reaches the over‑discharge protection voltage.
Capacity test: Discharge the battery at a standard current (e.g., 0.5C or 1C) through the discharge port to the cutoff voltage, recording the discharge capacity.
Rate discharge test: Verify the battery's capacity retention and voltage plateau at different discharge rates (e.g., 1C, 2C, 3C, 5C).
Simultaneous charge/discharge test: Simulate actual operating conditions by charging the battery through the charge port while simultaneously applying a load through the discharge port, verifying system stability and thermal management under simultaneous operation.
Protection function verification
Independent protection verification: Verify that the charge port provides only overcharge protection (no discharge protection when discharging from the charge port), and the discharge port provides only over‑discharge protection (no overcharge protection when charging from the discharge port).
Reverse‑connection test: Verify that the protection circuit operates correctly when the charge or discharge port is connected in reverse.
Communication function test: For separate‑port batteries with communication interfaces (e.g., CAN, RS485), verify proper data exchange between the BMS and the test system.
Data recording and analysis
The following key parameters should be recorded during separate‑port battery testing:
Charge parameters: charge voltage, charge current, charge capacity, charge time, temperature rise during charging.
Discharge parameters: discharge voltage, discharge current, discharge capacity, discharge time, temperature rise during discharging.
Protection parameters: overcharge protection voltage, over‑discharge protection voltage, overcurrent protection threshold, protection response time.
Simultaneous operation parameters: charge power, discharge power, system temperature rise, voltage stability.
Separate‑port design: The natural choice for high‑rate scenarios
Separate‑port design reflects the shift from "general‑purpose" to "scenario‑specific" battery design. In high‑discharge, low‑charge industrial applications, it optimizes cost, resistance, thermal performance, and flexibility while supporting simultaneous operation. It is already standard in AGV/AMR, forklifts, high‑rate storage, and specialty equipment. Testing such batteries requires equipment with independent control and flexible wiring, and demands a solid understanding of separate‑port principles. As these markets continue to grow, mastery of separate‑port design, purpose, and testing has become essential for battery R&D, production, and quality professionals.
