Battery pack design, without the guesswork

CellBuilder is a design tool for custom lithium battery packs. You choose a cell, set how many sit in series and in parallel, and arrange them into rows. From there the app works out the pack's voltage, capacity and stored energy, lays the cells out to scale with offset honeycomb packing where you want it, sizes the nickel strip and busbars for your series interconnects, checks whether your chosen BMS can actually serve the pack, and estimates how hot the cells will run at the current you intend to draw. Every figure comes from the same model, so changing one value updates all of them at once.

It is built for people who assemble packs rather than browse them: e-bike and e-motorcycle builders, EV conversion hobbyists, caravan and off-grid solar installers, robotics and drone teams, and small workshops quoting a one-off pack. If you have ever sketched a cell layout on paper and then discovered the enclosure was two millimetres too short, or wired a pack only to find the BMS tripped under load, this tool exists for the step before you spend money.

CellBuilder is designed and built by the CellBuilder team, an independent group of battery and software engineers who were tired of spreadsheets. It is funded by CellBuilder Pro, the paid tier that adds performance and thermal analysis, the busbar advisor, cloud-saved designs and the comparison dashboard — which is why the core configurator stays free and needs no account. When a model rests on an assumption, we state it in the interface: usable energy is reported at an 80% depth of discharge, and voltage sag and temperature are evaluated at the pack's continuous rating.

Nothing here replaces testing a finished pack. What it does is catch the mistakes that are cheap to fix on screen and expensive to fix with a spot welder.