Battery pack calculator
Enter the series and parallel count you are planning and this works out what that pack actually is — how many cells, what nominal voltage, how much capacity — and which of our 110 housings will hold it. No email required.
Your configuration
21700 cells are wider, so a housing takes fewer of them — the same case holds noticeably less capacity.
Series count sets the voltage. 13S is what almost every 48 V build uses.
Parallel count sets the capacity and the current. More P means more cells and a bigger housing.
13S5P on 18650
| Cells | 65 |
| Nominal voltage | 46.8 V |
| Capacity | 17.5 Ah |
| Energy | 819 Wh |
Capacity assumes 3.5 Ah per 18650 or 5.0 Ah per 21700, which is typical for the cells suppliers actually stock. Your own cells will differ — the cell count and voltage are exact, the capacity is a working figure.
Housings that take a 13S5P pack
Sorted by how much room they leave after your pack, so the first ones give you space for a BMS and the wiring. The ceiling shown is for the cell format you selected.
How the numbers are worked out
Cells is series multiplied by parallel. A 13S5P is 13 groups of 5, so 65 cells.
Voltage is the series count times the nominal cell voltage. Li-ion cells are 3.6 V nominal, which is why 13S is called 48 V even though it charges to 54.6 V and sits nearer 46.8 V for most of its discharge.
Capacity is the parallel count times the capacity of one cell. Six cells in parallel of 3.5 Ah gives 21 Ah. This is why the parallel count is the number that decides how big a housing you need, and the series count usually is not.
Energy is voltage times capacity in amp-hours, which gives watt-hours — the figure to use when comparing packs of different voltages.
The one thing this calculator cannot tell you is whether the pack will physically close, because that depends on the interior of the housing rather than its ceiling. A 13S BMS is longer than the 10S board most of these moulds were designed around, and that is the usual reason a build that “fits” on paper does not fit in practice. There is a guide on why a 13S5P pack will not fit.
Related
- Case selector — same idea, entered as a cell count
- 13S4P vs 13S5P vs 13S6P — what each configuration is
- Reention and Polly case sizes — what the industry names mean
- Compare the six formats — including which is wrong for a build
Send us the pack and we will confirm the fit
Cell format, series and parallel count is usually enough to answer the same day. If the answer is that none of our moulds fit, we will say so rather than sell you the nearest thing.