Battery S/P Configuration Calculator | BatteryPackCalc

How to Use the Pack Configuration Tool

Enter the nominal, maximum, and minimum voltage of a single cell along with its capacity in amp-hours, then set the number of cells you plan to wire in series (S) and in parallel (P). The presets fill these in for common chemistries — an 18650 generic cell, for example, loads 3.7 V nominal, 4.2 V full, 2.5 V empty, and 2.5 Ah — but you can switch to Custom and type values straight off your own datasheet. Series multiplies voltage while parallel multiplies capacity, and the layout you choose has to physically fit inside the enclosure you intend to build.

The pack voltages scale directly with the series count: pack nominal is S × cell nominal, pack maximum is S × cell maximum, and pack minimum is S × cell minimum. Capacity scales with the parallel count, so pack capacity is P × cell capacity, and total energy is simply pack nominal voltage × pack capacity. A 10S3P pack of 3.6 V 3 Ah cells therefore comes out to 36 V nominal, 9 Ah, and 324 Wh, built from 30 cells in total. The honeycomb SVG below the results redraws live as you change S and P so you can sanity-check the physical arrangement before committing to a weld pattern.

The voltage window matters as much as the nominal figure. That same 10S pack of 3.6 V cells reaches 42 V fully charged (10 × 4.2) and should not be drained below 25 V (10 × 2.5), and your charger and BMS must be matched to those endpoints rather than to the nominal value. Watt-hours, not amp-hours, are what determine range and runtime, so when you compare two layouts compare their Wh. Leave a little headroom in the enclosure for cell holders, nickel busbars, and the BMS, and remember that a taller series string needs proportionally more balancing leads.