The short answer
Every lithium pack is described as XSYP — X cells in series, Y in parallel. Series multiplies voltage; parallel multiplies capacity and current. So sizing a pack is really two questions:
- S =target voltage ÷ 3.6V (the nominal voltage of one Li-ion cell), rounded to a whole number.
- P =target capacity (Ah) ÷ one cell's capacity (Ah), rounded up.
Total cells = S × P. That's it. The hard part is just picking your targets — so let's make that interactive.
Try it: pack calculator
Open full page →Pick a cell, set your target voltage and range, and watch the series/parallel layout update. Then open the result in the full simulator to model voltage sag, temperature, and runtime under load.
Target pack nominal voltage (e.g. 36, 48, 52).
Target energy in watt-hours.
- Nominal voltage
- 46.8 V
- Capacity
- 12.0 Ah
- Energy
- 562 Wh
- Cell count
- 52
- Total weight
- 2.37 kg
- Max continuous
- 60 A
Worked examples
Three common builds. Each one opens in the simulator so you can see exactly how the cell behaves under that load.
Capacity vs. current: which cell?
Two cells with the same physical size can be tuned very differently. A high-capacity cell stores more energy (more range) but can't deliver as much current; a high-drain cell hits big current targets with fewer parallel groups but stores a little less. Your application decides:
- • Ebikes / commuters: favor capacity. A 3000–3500mAh cell maximizes range at moderate current.
- • Esk8 / drones / tools: favor current. High-drain cells let you hit the amp target without ballooning the cell count.
Not sure which cell fits? Browse the cell database (with real lab-tested discharge curves) or run a side-by-side comparison.
Common mistakes
- • Sizing on capacity alone. Always check that P × cell max current clears your peak draw, or the pack sags and overheats.
- • Mixing cells. Use identical cells across the whole pack — mismatched capacity or internal resistance causes uneven aging and hot spots.
- • Ignoring voltage sag. Nominal Wh isn't usable Wh under load. Model it in the simulator before you build.
Frequently asked questions
How many 18650 cells do I need for a 48V ebike battery?
A 48V (nominal ~48.1V) pack uses 13 cells in series (13 × 3.6V = 46.8V nominal, 54.6V full). The number in parallel sets your range: 4 cells in parallel (13S4P) of a 3000mAh cell like the Samsung 30Q gives roughly 12Ah / 562Wh, enough for ~25–30 miles on a typical ebike.
Does adding cells in parallel increase voltage?
No. Parallel cells add capacity (amp-hours) and current capability, not voltage. Voltage is set entirely by how many cells are in series. To raise voltage you add cells in series; to add range you add cells in parallel.
How do I calculate the number of cells from a target range?
Estimate energy first: range × Wh-per-mile (≈20 Wh/mi for an ebike, more for heavier loads). Divide that by the pack's nominal voltage to get amp-hours, then divide by a single cell's capacity and round up to get the parallel count. Multiply series × parallel for the total cell count. The calculator on this page does all of this for you.
Is it better to use higher-capacity or higher-current cells?
It depends on the build. High-capacity cells (e.g. 3500mAh) maximize range for low-to-moderate current draws like ebikes. High-drain cells (e.g. Molicel P42A) deliver more current per cell, so you can hit a current target with fewer parallel groups — better for e-skateboards, drones, and power tools.