Battery Pack Calculator — Series and Parallel Configurations
Calculate voltage, capacity (Ah/Wh), and cell count for any battery pack configuration.
Design Li-ion, LiFePO4, or NiMH packs for EVs, solar, and DIY projects.
Series vs. Parallel Connections Batteries can be connected in two fundamental ways. Cells in series add their voltages together while keeping the capacity (Ah) the same — like stacking AA batteries in a remote control, each one adds its 1.5V to the total. Cells in parallel add their capacity (Ah) while keeping the voltage the same — like two identical batteries side by side sharing the load. A combination of both (series-parallel, or “xSyP”) achieves any desired voltage and capacity.
The S and P Notation Battery pack configurations are described as “xSyP” — for example, 4S3P means 4 cells in series and 3 such strings connected in parallel. The result: voltage = 4 × cell voltage, capacity = 3 × cell capacity, total cells = 4 × 3 = 12. A 4S3P pack of 3.7V / 3.5Ah cells gives 14.8V / 10.5Ah = 155.4Wh.
Cell Chemistry Voltages Lithium-Ion (Li-ion): 3.6–3.7V nominal, 4.2V fully charged, 3.0V minimum discharge. Used in phones, laptops, and consumer electronics. Lithium Iron Phosphate (LiFePO4): 3.2–3.3V nominal, 3.65V full, 2.5V minimum. Safer, longer cycle life (2,000+ cycles vs 500 for Li-ion), slightly lower energy density. The preferred choice for solar storage and EVs where safety and longevity matter. NiMH: 1.2V nominal — still used in power tools and consumer AAs.
A Famous Example The original Tesla Model S used 7,104 Panasonic 18650 cells in an 86S82P configuration (approximately), delivering around 400V and 85 kWh. The Model 3 Long Range uses 4,416 cylindrical cells. These packs are engineering masterpieces — thousands of small cells monitored individually by sophisticated battery management systems.
The BMS Is Not Optional A Battery Management System (BMS) is absolutely required for any lithium chemistry pack. The BMS monitors each cell’s voltage and temperature, prevents overcharging (which causes fire), prevents over-discharge (which permanently damages cells), balances cells to equalize voltages, and provides short-circuit protection. Never build or charge a lithium pack without a proper BMS.
Wh Is the Real Measure of Energy Amp-hours (Ah) measure charge, not energy. Two packs with the same Ah but different voltages hold very different amounts of energy. Watt-hours (Wh = V × Ah) is the correct unit for comparing energy storage across different systems — and it’s what determines how long your device runs.