Building a custom lithium battery pack requires selecting the right series and parallel arrangement, also known as S×P configuration. This determines the pack voltage, total capacity in Ah, and maximum discharge current capability. This tool helps you calculate all these values based on common cell formats used in eBike and DIY lithium battery projects.
How Lithium Battery Series and Parallel Works
Lithium battery packs combine multiple individual cells to form a larger unit. Cells in series (S) add voltage, while cells in parallel (P) add capacity and increase current capability. The combination determines the total energy stored (Wh) and the safe discharge rate.
- More series → higher voltage
- More parallel → higher capacity (Ah)
- Larger P → more discharge current capability
- Total Wh = Voltage × Ah
Example: 13S4P = 48V pack using 52 individual 18650 cells.
Calculated Values in This Builder
This calculator estimates:
- Total pack voltage (Nominal)
- Total capacity (Ah)
- Total energy (Wh)
- Maximum continuous discharge current
- Typical range estimation based on Wh
This calculation helps determine compatibility with your eBike controller current limits and motor power requirements.
- 18650: 3.6V, 2500–3500 mAh
- 21700: 3.6V, 4000–5200 mAh
- Pouch: 3.7V, 5–15 Ah
21700 cells are rapidly replacing 18650 in high-performance eBikes due to higher energy density and discharge capability.
Safety Considerations in DIY Pack Building
Lithium battery building requires knowledge of balancing circuits, cell matching, and proper insulation. Always use a certified BMS, appropriate fusing, and nickel welding designed for high current flow.
- Spot welding instead of soldering
- Individual cell testing is recommended
- Always include a BMS
- Use temperature protection where possible
- Match cells by capacity and internal resistance
Frequently Asked Questions
Q: What does 13S4P mean?
A: 13 cells in series and 4 parallel. This layout determines battery voltage and total capacity.
Q: Is higher series always better?
No. Higher voltage increases speed but must match controller and motor ratings.
Q: Do more parallel cells increase motor power?
More parallel cells increase discharge current capability and reduce voltage sag under load.
Q: Can I mix different cells?
No. Always use matched cells with identical age, chemistry, and capacity.
Q: Do I need a BMS?
Yes. A Battery Management System is mandatory for balancing and safety.
