Preconditioning a Battery for Fast Charging: An OEM Readiness Plan

“Pre-conditioning” a battery for fast charging refers to adjusting the battery’s thermal state before the charging process begins. For electric buses or trucks, the key issue is whether the battery can reach the required state of charge while the vehicle is parked. Simply turning on the heater, using warm coolant, or running the compressor is not sufficient to ensure the battery is ready for charging.

Battery suppliers set corresponding charging limits. Vehicle engineering teams must coordinate the battery management system (BMS), thermal management system, vehicle control unit, and charging interface accordingly. Depending on the battery’s initial state, thermal pre-conditioning may involve heating or cooling.

The Volvo Group discusses the relationship between battery temperature and charging performance in its thermal management overview. However, this background information does not directly define a universal “charging temperature” or “pre-conditioning duration”; specific values must be determined based on the selected battery model and validated vehicle configuration.

The approach should start with the “charging stop” phase, rather than focusing solely on the heater’s rated power.

Even if a vehicle is equipped with sufficient heating capacity, it may still be unable to complete the intended charging task if it arrives too late. Therefore, the driving route and charging plan must be clearly defined before establishing a thermal preconditioning strategy.

Items to be recorded include: the estimated State of Charge (SOC) upon arrival, battery temperature distribution, the target SOC at the planned departure time, and the available parking duration at the charging station. Additionally, limitations of the charging equipment and the site’s power supply capacity must be considered—the thermal management system cannot eliminate constraints imposed by the charging station or the site’s electrical infrastructure.

Take a 20-minute stop as an example: if connecting and authorization take 3 minutes, and departure preparations take 2 minutes, only 15 minutes remain for actual charging. This is merely a scheduling example and does not imply that all batteries can reach their expected charging targets within 15 minutes. Some operational steps can be performed concurrently; when calculating, one should refer to actual operational workflows rather than simply treating each step as a completely sequential process and adding them up.

The engineering task is to determine: how much of the thermal management preparation can be completed before the vehicle arrives, how much processing is still required after connection, and whether the remaining charging time is sufficient. If an energy source on which a particular solution relies is unavailable before the vehicle arrives, that solution must be revised before hardware selection takes place.

Clarify the specific meaning of the “ready” signal.

Distinguish between the following three states: the thermal management equipment has received a request; the coolant condition is approaching the target value; and the Battery Management System (BMS) permits the required charging current. These states correspond to different components of the system.

Coolant sensors cannot monitor every individual battery cell. Similarly, the charging permission signal may only allow a partial current flow, failing to reach the power level required for charging according to the established trip plan. Consult the battery supplier to clarify which measured values and constraints determine charging acceptance capability, including relevant temperature differentials and State of Charge (SOC) requirements.

Clarify the ownership and responsibilities for each signal. Determine who initiates the readiness request, who approves charging, who reports constraints, and who terminates or changes the thermal management mode. The mutually agreed-upon control specifications should clearly define response mechanisms for data loss or data latency. Do not assume that the EVLINK controller will automatically execute a specific command or fallback logic unless this has been specifically confirmed through configuration.

Map out the entire process from vehicle arrival to departure.

It is recommended to use project-specific timing logs to identify potential coordination gaps between controllers. The following content is provided solely as a planning reference and is not a mandatory standard.

For each conversion, the corresponding “request” and “acknowledgment” information must be clearly identified. If a command has been sent but not received (or accepted), it should not be included in the test report as an achieved operational state.

Thermal limitations should be distinguished from other types of limitations.

If charging performance falls short of expectations, the specific limiting factors should first be identified. Battery overcooling, overheating, or uneven temperature distribution each require different troubleshooting approaches; if the limitation stems from the site’s power cap or the charging equipment’s own limitations, a separate level of analysis is required.

Compare the BMS (Battery Management System) limit values, charging equipment output power, and thermal management feedback data after aligning the timelines. If the power allowed by the BMS exceeds the actual output power of the charging equipment, simply increasing heating capacity may not resolve the limitation. If the thermal management system indicates that the coolant is in good condition but there are discrepancies in the response across different areas of the battery, it is essential to first check the temperature distribution and measurement boundaries before concluding that the entire battery pack is in an ideal state.

The “Battery Thermal Management System (BTMS) Thermal Load Worksheet” can assist in defining thermal loads, while the “Rated Operating Conditions Guide” explains why relying solely on “nominal capacity” is insufficient for a comprehensive performance evaluation. Neither of these tools can replace the charging limit requirements set by the battery supplier.

Verify the vehicle’s complete stop state under typical operating conditions.

Prior to testing, agree on the initial conditions and acceptance criteria. The scope should cover: expected arrival temperature and state of charge (SOC), available preparation time window, charging equipment capacity, and vehicle electrical limitations. Using a unified time reference, record the battery temperature distribution, relevant coolant temperature and flow rate, thermal management commands and feedback, charging authorization status, actual charging power, and elapsed time.

Evaluate the transition from driving to charging mode, as well as the steady-state phase during charging. Observe the system’s response when charging demands change or the preparation phase ends. Repeat tests under both cold and hot arrival conditions according to the established validation plan; successful completion of cold-start validation alone does not guarantee that the system will achieve expected performance in high-temperature environments.

Never disable protective functions in order to obtain an ideal charging curve. If charging is limited, retain the original controller logs and clearly identify which subsystem triggered the limitation. Discrepancies between projected and measured performance must be resolved before finalizing the charging strategy.

Prepare an “Electric Vehicle Charging Thermal Readiness Assessment” (EVLINK thermal readiness assessment).

Provide the charging conditions permitted by the battery supplier, driving routes and parking timelines, thermal load information, coolant requirements, installation constraints, and available power supply conditions. Clearly define the controller’s responsibilities and signal list; refer to the “Battery Thermal Management System (BTMS) CAN Bus Integration Guide” to assist in organizing the relevant content.

Commission EVLINK to evaluate the proposed BTMS and heating configuration based on the above input information. Require a clear definition of the operating conditions corresponding to each capacity metric, and identify the vehicle-level test items that still need to be conducted. Provide the charging timeline and thermal management requirements to ensure that discussions are based on actual “readiness time windows” rather than solely on the rated power of the heaters.