Example Data Table
| Use Case |
Cell Voltage |
Cell Ah |
Target Voltage |
Target Energy |
Consumption |
| City EV |
3.2 V |
6 Ah |
320 V |
40 kWh |
135 Wh/km |
| Family EV |
3.7 V |
5 Ah |
400 V |
75 kWh |
165 Wh/km |
| Performance EV |
3.7 V |
5 Ah |
720 V |
100 kWh |
210 Wh/km |
Formula Used
Series cells: S = target pack voltage ÷ cell nominal voltage
Parallel strings: P = target energy Wh ÷ (S × cell voltage × cell Ah)
Pack voltage: Vpack = S × Vcell
Pack capacity: Ahpack = P × Ahcell
Nominal energy: kWh = Vpack × Ahpack ÷ 1000
Usable energy: usable kWh = nominal kWh × usable SOC × reserve factor
Peak current: I = peak motor watts ÷ nominal pack voltage
Pack resistance: Rpack = S × Rcell ÷ P
Voltage sag: Vsag = I × Rpack
Heat loss: heat watts = I² × Rpack
Range: range = usable Wh × drivetrain efficiency ÷ Wh per km
How to Use This Calculator
Enter the cell voltage, capacity, resistance, mass, and price. Add your target pack voltage and target nominal energy. Leave series and parallel fields empty for automatic sizing. Enter them manually when testing a fixed layout. Add consumption, efficiency, motor power, charger power, and C-rate limits. Press the calculate button. Review warnings before using any result in a real design.
EV Battery Pack Planning
An EV battery pack is more than a group of cells. It is a balanced electrical system. Voltage, capacity, current, mass, heat, and cost all affect the final design. A pack with the right energy may still fail if current demand is too high. A high voltage pack may also need stronger insulation, safer service rules, and better contactor selection.
Why Series And Parallel Matter
Series cells raise voltage. Parallel cells raise amp hour capacity. Together, they set total pack energy. The calculator can estimate both values from target voltage and target energy. You can also enter exact counts when a design already exists. This helps compare a planned layout with a known module stack.
Usable Energy And Range
Nominal energy is not the same as usable energy. EV packs avoid full charge and deep discharge to protect cells. A degradation reserve also protects range after aging. The calculator applies usable state of charge and reserve values. It then estimates driving range from energy, drivetrain efficiency, and vehicle consumption.
Current, Sag, And Heat
Peak motor power creates pack current. The current depends on pack voltage. Higher voltage usually lowers current for the same power. Cell internal resistance creates voltage sag. It also creates heat during strong acceleration or heavy load. The calculator estimates pack resistance from cell resistance, series count, and parallel count. Heat output helps size busbars, cooling plates, and safety margins.
Charging And Safety Checks
Charge current depends on charger power and pack voltage. The charge C rate shows how hard the cells are charged. Discharge C rate compares motor demand with cell capability. A design is stronger when both rates stay below safe cell limits. Real packs still need fuses, contactors, isolation monitoring, balancing, enclosure design, and thermal validation.
Cost And Practical Use
Cell price gives a quick cell cost estimate. Added system cost covers BMS, wiring, case parts, cooling, and contactors. Mass estimates help compare energy density. Record each assumption before comparing options. Small input changes can shift cell count, current stress, and thermal load. Review margins before buying parts or building modules. Use results as an early engineering guide. Confirm final designs with cell datasheets, standards, tests, and qualified electrical review.
FAQs
1. What does S and P mean in a battery pack?
S means series cells. It raises voltage. P means parallel cells. It raises amp hour capacity. A 108S30P pack has 108 cells in series and 30 parallel cells in each group.
2. Should I enter series and parallel counts manually?
Leave them blank for automatic sizing. Enter them manually when checking an existing module layout, salvage pack, or fixed enclosure design.
3. Why is usable energy lower than nominal energy?
EV packs usually keep charge and discharge limits. This protects cell life. The calculator also subtracts a degradation reserve, so the estimate is more realistic.
4. What is voltage sag?
Voltage sag is the temporary voltage drop under load. It depends on current and pack resistance. Large sag can reduce power and increase heat.
5. What is C-rate?
C-rate compares current with battery capacity. A 100 Ah pack at 1C delivers 100 A. A 2C load delivers 200 A.
6. Can this calculator replace cell datasheets?
No. It is an estimate tool. Always confirm current limits, temperature limits, cycle life, charge rules, and safety data with official cell datasheets.
7. Why does higher voltage reduce current?
Power equals voltage times current. For the same motor power, higher pack voltage needs less current. Lower current can reduce cable loss and heat.
8. Is the cost estimate final?
No. It includes cell cost and a simple system cost. Real packs also need busbars, fuses, contactors, sensors, cooling, enclosure parts, labor, and testing.