Lithium-Ion Battery Pack Design Simulation for Battery Swapping

Lithium-Ion Battery Pack Design Simulation for Battery Swapping

Introduction

In a swapping network, the battery pack is no longer a part of one vehicle. It is a shared asset that moves between vehicles, chargers and stations, sometimes several times a day, handled by riders, drivers and station staff.

That changes the engineering. A fixed pack in a scooter is designed for one vehicle and one owner. A swappable pack must work in every compatible vehicle, tolerate rough handling and thousands of connector mating cycles, charge safely in a station cabinet straight after a hard ride, and remain healthy for years under an operator’s economics, where every lost cycle is lost revenue.

Simulation helps teams test many of those questions before building packs and stations. The IST Li-ion Battery Simulator is a browser-based workbench that takes a pack from application targets through sizing, cell modelling, thermal analysis, BMS logic, ageing and a design report, with nothing to install.

Where Swappable Packs Are Used

• Electric two-wheelers: Commuter scooters and delivery bikes, where a swap takes less time than a charge.
• Electric three-wheelers: E-rickshaws and cargo three-wheelers running long daily distances.
• Fleet and delivery vehicles: Operators who cannot afford vehicles idling on chargers.
• Light commercial vehicles and equipment: Larger swappable modules for depot and route-based use.
• Station-side and hybrid use: Packs that can double as stationary storage when idle.

What Makes Swappable Packs Different

The main design pressures are:

• Interchangeability: Voltage window, current limits and communication must suit every vehicle and charger in the network.
• Handling robustness: Packs get dropped, knocked and stored in all conditions.
• Connector reliability: Contact resistance, heating and wear at the interface affect safety and range.
• Weight: A pack someone must lift by hand cannot be too heavy.
• Fast turnaround charging: Stations want packs ready quickly, which raises charge rates and heat.
• Fleet-level ageing: The operator carries the battery’s lifetime cost.
• Safety across a shared system: One poor pack can affect a station cabinet or a vehicle.

Step 1: Define the Application

The simulator begins with Define Application: voltage window, energy capacity, continuous and peak discharge power, peak duration, charge power, ambient range, IP target, cooling method, weight budget, envelope and standards. The guide lists application types including 2-Wheeler and 3-Wheeler, which select the vehicle model, default drive cycle, usage profile and standards (AIS-156 for L-category vehicles). There is no swapping-specific type described, so choose the closest vehicle type and set the other fields manually.

Some fields deserve extra thought for swapping:

• Voltage window: It must fit every vehicle controller in the network, not just one.
• Weight budget: Treat this as a handling limit, not only a performance one.
• IP target: The guide uses IP67 as the AIS-156 water-immersion check for vehicles, and a swappable pack that sits outside a vehicle between swaps deserves the same seriousness.
• Charge power: Set this to the station charger’s rate, since fast turnaround drives it.

As the guide advises, fill the voltage and power targets carefully, because the most useful output is the list of targets your chosen cell and BMS cannot meet.

Step 2: Choose the Cell and BMS

The database holds cylindrical, prismatic and pouch cells, plus BMS boards, busbars, fuses, connectors and other parts, and you can import your own as .dat files. For swappable packs, the selection criteria that matter most are:

• Chemistry: The guide describes LFP as the safest and longest-lived common option, which suits packs that are cycled hard every day. NMC offers more energy per kilogram, which helps the handling-weight limit.
• Format: Fewer, larger prismatic cells mean fewer welds and a simpler BMS. Smaller cylindrical cells give flexibility in shape and some fault tolerance.
• Cycle life and conditions: The ageing model is calibrated to the cell’s datasheet cycle-life rating, so check the stated conditions against how your network will actually use the cell.
• DCIR and temperature limits: These set heat, voltage sag, and how comfortably the pack handles fast charging and hot days.

On the BMS side, the simulator checks that the series range covers your Ns, that OVP and UVP sit inside the cell window, that continuous and peak over-current limits fit the vehicle and charger, and that the over-temperature trip sits within the cell’s limits. For swapping, also check the communication protocol (CAN 2.0 or RS485) against the vehicles and chargers, since a pack that cannot talk to its host is not interchangeable.

Step 3: Size the Pack

In Pack Configuration you enter series cells, parallel cells and module count, or ask the simulator to suggest them from your targets. It returns the cell model, a cell-to-BMS check, pack sizing, a pass/warn/fail check against your targets and a standards checklist.

An illustrative example. The numbers below use a hypothetical 3.2 V, 50 Ah, 1.2 mΩ, 0.9 kg prismatic LFP cell and an assumed scooter load. They are my own back-of-envelope calculations with the guide’s formulas, not simulator output, so substitute your own cell and vehicle data.

• Configuration: 16S1P
• Nominal voltage: 16 × 3.2 = 51.2 V
• Energy: 51.2 V × 50 Ah = 2.56 kWh, or about 2.3 kWh usable at 90%
• Pack resistance: 16 × 1.2 mΩ × 1.10 ≈ 21 mΩ
• Mass: 16 × 0.9 kg = 14.4 kg of cells; dividing by the guide’s 0.75 prismatic packing ratio gives roughly 19 kg, or about 133 Wh/kg at pack level

That last figure is the swapping-specific warning: roughly 19 kg is already a heavy lift for one person, and every extra kilogram of enclosure or cell makes swaps slower and less comfortable.

Now the load checks, using an assumed 3 kW continuous and 6 kW peak:

• Continuous (about 59 A, or roughly 1.2C): about 73 W of heat inside the pack.
• Peak at minimum voltage: the guide computes minimum voltage as Ns times cell cut-off, which for 16 cells at 2.5 V is 40 V, so 6 kW needs about 150 A, or 3C. The cell’s pulse rating and the BMS peak limit both need to support that, and the targets check would flag it if not.
• Station charging at 1C (50 A): about 53 W of heat. At 0.5C it falls to about 13 W. Charging faster turns packs around quicker but costs thermal margin and life, which is a trade-off simulation can quantify.

Step 4: Model the Cell

The BDS Cell Modeling module builds the models behind later analysis:

• HPPC-based equivalent-circuit extraction gives R0 and two RC pairs, which determine voltage sag under load and recovery after it.
• EIS-based fitting and a reduced-order P2D (SPMe-type) electrochemical solver, benchmarked against PyBaMM’s DFN model within about 2 mV RMS up to roughly 6C.
• Joint parameter identification from a measured voltage trace.

When test data is not available, the simulator auto-generates inputs from the selected cell, labelled as synthetic. For a network that will run thousands of packs, replacing these with measured data for your exact cell is one of the most valuable validation steps.

Step 5: Thermal Analysis for Riding and Charging

A swappable pack sees two thermal situations: discharge in the vehicle, and charging in a station, often right after a ride when the pack is already warm.

The thermal tools include:

• Conjugate heat transfer and coolant flow and pressure drop calculations for cooled designs.
• 3-D cooling simulation for natural convection, forced air through cell gaps or a liquid cold plate. It reports maximum temperature, cell-to-cell ΔT, energy balance, and for forced cooling the pressure drop and fan or pump power. The guide suggests targets of Tmax at or below 45 °C and ΔT at or below 5 K.
• Thermal imaging live view, a staged cooling controller across eight modules, to see how a cooling strategy responds.

For swapping, the useful comparison is between charge rates: run the 3-D cooling card at a gentle and at a fast charge current and see how much margin you lose. The guide also notes typical charge temperature limits of roughly 0 to 45/55 °C, which matters for stations in cold or very hot locations, and the BMS under-temperature charge test in the safety cards checks the logic.

Two honest limits apply. First, the 3-D cooling tool is not a Navier-Stokes solution, so detailed airflow in a station cabinet needs full CFD or a test. Second, it models the pack, not the station cabinet’s own thermal management, which you will need to assess separately.

Step 6: Thermal Runaway and Propagation

Swappable packs are stored and charged in groups, so one failure has more places to spread. The propagation module models a module as a network of cells with per-cell abuse kinetics, internal short after separator melt, venting, and heat transfer through gaps, barriers, busbars and radiation.

You choose the trigger, test SOC, cooling state and barrier (none, 2 mm air, 1 mm mica, 2 mm aerogel or 3 mm ceramic fibre). Results show how many cells enter runaway, the time between the first and second event, and an automatic barrier comparison. That helps you find the lightest barrier that stops propagation or buys the required time, which matters for a pack whose weight is also a handling limit. An ARC-style runaway analysis, auto-generated from the selected cell, shows self-heating onset and the margin to the BMS over-temperature trip. The guide’s 5-minute proxy comes from the L-category vehicle standard, so confirm the final design with physical propagation testing. This simulation covers one pack, not the spread between neighbouring packs in a charging cabinet.

Step 7: BMS Design and Fault Testing

For a shared pack, the BMS carries more responsibility: it protects the pack, talks to many hosts and reports faults to the station and vehicle. The verification tools include:

• Protection and balancing simulation covering OV, UV, over-current, short circuit, over-temperature and sensor faults.
• SOC and SOH estimation (EKF SOC with resistance tracking), which matters because riders and operators both rely on remaining-range and health data.
• Closed-loop drive-cycle simulation on standard cycles. For two- and three-wheelers the guide’s relevant cycles are MIDC Part-1 urban and WMTC Class 3, and the report selects MIDC Part-1 automatically for 2W and 3W.
• Fault-injection matrix covering over-charge, over-discharge, over-current, external short, cooling failure, charge at low temperature, open NTC and open pre-charge resistor, each with detection latency against requirement and a diagnostic code.
• Code generation with SIL and HIL, producing C code, a CAN message set with a DBC file and test vectors. A SIL pass means the generated C reproduces the simulator’s logic at every step. The guide is clear that this is template-based, MISRA-oriented, not certified and has no ISO 26262 tool qualification, and that short-circuit protection must also exist in hardware.

For swapping specifically, the CAN database matters, since every vehicle and charger in the network needs to interpret the pack’s messages the same way. The simulator generates one, but agreement between manufacturers on message content is a network design decision outside the tool.

Step 8: Electrical Design and the Connector

The Circuit Design tab derives design current, a temperature-derated fuse, busbar cross-section (about 3 A/mm² for copper), pre-charge sizing and minimum isolation, and checks fuse breaking capacity against short-circuit current. It also provides DFM module geometry and tolerance stack-ups, plus module wiring diagrams with balancing taps and NTC positions, exportable as SVG.

The guide’s resistance formula includes a 10% allowance for busbars, welds and contactors, but a swappable connector deserves its own thought. As a rough illustration, a connector pole with 1 mΩ of contact resistance carrying 60 A dissipates about 3.6 W, and at 150 A peak about 22 W, concentrated in a small volume. Contact resistance also tends to rise with wear and contamination over many mating cycles. The simulator does not model connector wear, so treat connector heating, locking and cycle-life as items for dedicated testing, using the simulator’s current and heating figures as the starting point.

Packs above 60 V are treated as class B, with contactor and pre-charge circuits in the schematic, while lower-voltage packs use BMS MOSFETs. If your swappable pack connects to a capacitive load on insertion, check inrush behaviour with your vehicle supplier.

Step 9: Ageing and Fleet Economics

For an operator, battery life is the largest cost line, so ageing prediction has direct financial value.

• Calendar and cycle ageing models SEI growth, particle cracking and lithium plating, with plating risk increasing in cold or fast-charge conditions. You set years, cycles per day, depth of discharge, charge and discharge C-rates, rest SOC, ambient mean and seasonal swing, cell temperature rise, charging temperature and the end-of-life SOH threshold. It returns end of life in years and equivalent full cycles, SOH and resistance curves, a loss breakdown, a plating warning and a calendar-only reference. For swapping, you can compare a gentle charging strategy against a fast one and see how many months of life it costs.
• Warranty and life prediction runs many simulated units with spread in usage, using cities with approximate Indian climate normals. It reports expected claim rate, SOH at end of warranty (P5, median and P95), claims by city and the longest warranty that keeps claims under your target. That fits an operator pricing a battery-as-a-service plan.

The guide cautions that ageing results are a screening estimate until fitted to your own storage and cycling tests. For a network, start those tests early, since refitting the model before committing to a warranty protects the business case.

Step 10: Safety Checks and the Design Report

The Safety & Compliance tab covers capacity, resistance, isolation, overcharge, short circuit, drop, shock, vibration and protection response time, then rolls them into a release decision where any failed or un-run gate blocks release. The drop and shock checks are particularly relevant to a pack that is carried and handled. The standards checklist includes AIS-156 for L-category vehicles, UN R100, UN 38.3 and IEC 62619. Requirements specific to swappable packs, swapping stations and interoperability are not built into the checklist, and policy and standards in this area may change, so confirm the current requirements with your testing agency and the relevant authorities.

Reports then runs the full chain and produces an A4 design report with the schematic, simulation results, standards checklist and bill of quantities.

Questions Simulation Helps Answer

• Does this pack fit the voltage window and current needs of every vehicle in the network?
• How heavy is too heavy for hand swapping, and what does a lighter pack cost in range?
• How much heat does fast station charging add, and what life does it cost?
• Does the BMS protect the pack and report faults correctly to both vehicle and station?
• What is the lightest barrier that stops one failing cell from spreading?
• How many months of life does a gentler charging strategy buy?
• What warranty can the operator offer at an acceptable claim rate?

What the Simulator Is, and Isn’t

It is a design and screening tool. Pack arithmetic follows standard formulas, while thermal, abuse, ageing and system models are reduced-order. It does not model connector wear, mechanical locking, station cabinet thermal management, swap logistics or fleet scheduling, and it does not replace the physical tests required for approval. Ageing results are a screening estimate until fitted to test data.

A sensible validation path:

1. Replace synthetic HPPC, EIS and ARC data with measured data for your chosen cell.
2. Test a prototype pack on vehicle and charger hardware, comparing temperature and voltage behaviour with the simulation.
3. Test the connector and housing separately for mating-cycle life, heating, ingress and drop.
4. Run SIL, then HIL, then hardware protection tests on the BMS across the vehicles and chargers it must work with.
5. Complete cell and pack certification tests with an accredited lab.
6. Start calendar and cycle ageing tests early, then refit the life model before making warranty or service-plan claims.

Conclusion

A swappable pack has to be good at being shared: light enough to lift, rugged enough to drop, compatible with everything it plugs into, and durable under constant charging. Simulation lets design teams test those compromises early, comparing cells, parallel counts, charge strategies, barriers and BMS settings before committing to tooling and stations.

Explore pack design at Academy of EV Technology and follow the step-by-step guide from mission targets to a full design report.