From a target voltage and an awkward envelope to a repairable, production-ready lithium-ion pack.
This guide is written for engineers and product teams who need a custom lithium-ion battery pack for an e-bike, a light electric vehicle, a robot, a marine application or a stationary storage project — and who do not want a generic, sealed off-the-shelf box. It walks through the decisions that drive the design, the trade-offs between cell formats and chemistries, and the workflow we use at MAKI to turn a sketch into a quoted, repairable pack.
Every numerical example below can be reproduced live in the MAKI Pack Configurator.
Before picking a cell, fix three numbers from the rest of the system:
From those three numbers, S, P and the choice of cell follow almost mechanically.
For the kind of small-to-medium packs MAKI builds (roughly 200 Wh to 10 kWh), the practical contenders are:
| Format | Dim (mm) | Typical capacity | Typical use |
|---|---|---|---|
| 18650 | 18 × 65 | 2.5–3.5 Ah | Legacy e-bikes, replacement packs, small power tools. |
| 21700 | 21 × 70 | 4.0–5.0 Ah | Default for new e-bike, e-scooter and robotics designs. Best Wh per €. |
| 4680 | 46 × 80 | 20–30 Ah | Larger LEVs, marine, stationary. Fewer cells, simpler mechanics. |
| Pouch | configurable | 10–60 Ah | Marine, drones, applications where pack thickness is the constraint. |
| Prismatic | configurable | 50–300 Ah | Stationary storage, large traction packs. |
Cylindrical cells (18650, 21700, 4680) are the easiest path to a repairable pack: they live in plastic cell holders, the busbars are accessible, and an end-of-life re-cell is a service operation rather than a re-engineering project. That is why they are the default in the configurator.
| NMC | LFP / LiFePO4 | NCA | |
|---|---|---|---|
| Nominal V/cell | 3.6–3.7 V | 3.2 V | 3.6–3.7 V |
| Energy density (Wh/kg) | 200–270 | 120–180 | 230–280 |
| Cycle life (full equivalents) | 500–1500 | 3000–6000+ | 500–1200 |
| Thermal stability | Moderate | Best | Moderate |
| Best for | Range-critical LEVs, drones | Fleets, ESS, safety-critical | Performance, niche |
The rough rule: if mass is the constraint (a frame-mounted e-bike battery, a backpack robot), pick NMC. If utilization is the constraint (a delivery fleet, a cycling stationary battery, anything where cycle life dominates total cost of ownership), pick LFP.
Worked example: a 48 V e-bike with a 700 Wh range target, using 21700 NMC cells of 5.0 Ah and 3.6 V nominal.
S = 13 (a 13S pack is 46.8 V nominal, 54.6 V full).P = 4 for headroom, giving 936 Wh at the cell level.The configurator does this calculation live and additionally checks whether 52 cells in a hex grid actually fit inside the pack outline you drew.
Custom packs exist because the outline is fixed — by a frame downtube, an under-seat tray, a robot's belly, the floor of a houseboat. Once the outline is drawn, the configurator hex-packs cells inside it, leaves the wall thickness and gap clearance you specify, and reports whether the requested S × P fits.
Two heuristics worth knowing:
The BMS sits flat against one wall of the pack and balances cells, enforces voltage, current and temperature limits, and exposes a state-of-charge estimate. Two practical decisions:
The SOC indicator (a small LED bar) is independent of the BMS and lives on a wall the user actually looks at.
The EU Battery Regulation (2023/1542) phases in removability and replaceability requirements through 2027. Beyond regulation, repairability has hard economic consequences: the structural housing, the BMS, the wiring harness and the connectors of a well-designed pack outlast their cells by a factor of two to three. A repairable pack means the customer pays for new cells at end of life, not for a whole new pack.
MAKI packs are designed to be opened by a qualified service partner, with bolted (not glued) housings, replaceable cell-blocks and documented service procedures.
The configurator output is a non-binding conceptual draft. Cell-holder layout, busbar sizing, thermal management, BMS firmware parameters, ingress protection and certification are finalised by MAKI engineering after the quote.
Open the configuratorThe MAKI Pack Configurator at custom.maki-batteries.com is a free, browser-based tool. No login. Outputs a PDF datasheet, a STEP CAD file, and a quote request to MAKI engineering.
13 cells in series, 4 in parallel, for 52 cells total. Voltage is 13 × cell voltage; capacity is 4 × cell capacity.
Yes — that is exactly what MAKI builds. Use the configurator to draft a pack that fits your frame and request a quote.
No. It is a non-binding conceptual draft, accurate enough for feasibility and quoting. Detailed design happens at MAKI after the quote request.
Energy, voltage and current numbers are within a few percent of the finished pack. Mass and volumetric density include a calibrated overhead for housing, BMS, wiring and connectors based on past MAKI designs.