Reference
Battery Sourcing Glossary
40 terms that show up in e-bike battery specifications and quotations, explained the way they actually matter to a buyer — with the arithmetic, not just the definition.
Electrical
- Amp-Hour (Ah) Charge capacity — how much current a pack delivers for how long — valid for comparison only between packs of the same voltage.
- C-Rate The charge or discharge current expressed as a multiple of the pack's capacity, so the same number means the same stress on any size of pack.
- Continuous vs Peak Current Two different ratings — what a pack sustains indefinitely, and what it delivers in short bursts — that must both be specified.
- Discharge Curve The plot of pack voltage against capacity used, whose shape determines how well a fuel gauge can estimate remaining charge.
- Internal Resistance The pack's own electrical resistance, which converts part of every amp drawn into heat instead of useful power.
- Nominal Voltage The average working voltage a pack is named for — distinct from its fully charged and fully discharged voltages, which is what equipment must actually tolerate.
- Series-Parallel Configuration (13S4P) The notation describing how cells are wired in a pack: S groups set voltage, P cells per group set capacity and current capability.
- Voltage Sag The temporary drop in pack voltage under load, caused by internal resistance — the reason a battery reads lower on a climb and recovers at rest.
- Watt-Hour (Wh) Total energy stored in a pack — voltage multiplied by amp-hours — and the only figure that compares packs across different voltages.
Cells & Chemistry
- Capacity Fade The permanent, gradual loss of a pack's storable energy over time and use — distinct from the temporary range loss caused by cold or heavy load.
- Cell Binning Sorting incoming cells into groups of matched capacity and internal resistance before assembly, so every parallel group starts equal.
- Cycle Life The number of full charge-discharge cycles a pack completes before its usable capacity falls to a stated fraction of the original, normally 80%.
- Depth of Discharge (DoD) How much of a pack's capacity is used before recharging — the single largest controllable influence on how many cycles it will deliver.
- Energy Density (Wh/kg) Energy stored per unit of mass or volume — the figure that decides whether a target capacity fits your frame and weight budget.
- Formation Cycling Controlled initial charge-discharge cycles that stabilise a cell's internal chemistry and establish its true baseline capacity.
- Lithium Plating Metallic lithium depositing on the anode instead of intercalating — caused mainly by charging cold or too fast, and largely irreversible.
- Self-Discharge The slow loss of charge in a pack sitting unused, from internal chemistry plus whatever the BMS electronics draw while idle.
- Separator The thin porous membrane keeping a cell's electrodes apart while letting ions pass — the component whose failure causes an internal short.
- Thermal Runaway A self-sustaining reaction where a cell generates heat faster than it can shed it, driving temperature and pressure up until the cell vents or ignites.
BMS & Control
- Battery Management System (BMS) The electronics that protect a lithium pack from overcharge, over-discharge, over-current and over-temperature, and keep its cell groups balanced.
- BMS Communication (UART / CAN) The data link that lets a pack report charge, health, and faults to a display or controller instead of being inferred from voltage alone.
- Cell Balancing The BMS function that equalises voltage across cell groups, preventing the weakest group from capping the capacity of the whole pack.
- Low-Temperature Charging Cutoff A BMS rule that blocks or limits charging below a set temperature, protecting cells from the permanent damage cold charging causes.
- Precharge Circuit A brief current-limited connection that charges a controller's capacitors before the main path closes, preventing a damaging inrush spark.
- State of Charge (SOC) How full the pack is right now, as a percentage of its present usable capacity — the figure a rider's display is trying to estimate.
- State of Health (SOH) Present usable capacity as a percentage of the pack's original rated capacity — how much of its life the pack has already spent.
Mechanical & Build
- Connector Pinout Which signal sits on which pin of a battery connector — the detail that decides whether a pack works or damages the bike it is plugged into.
- Hipot Test A high-voltage test between the pack's live circuit and its enclosure, verifying that insulation will not break down in service.
- IP Rating A two-digit code stating an enclosure's resistance to solid objects and to water — IP65 means dust-tight and protected against water jets.
- Nickel Strip The thin metal ribbon welded between cells to carry current — sized by thickness and width, and a common place to cut cost invisibly.
- Potting Compound Resin or silicone filling voids inside a pack to immobilise components against vibration and moisture — a choice with real trade-offs.
- Spot Welding Joining nickel strip to cell terminals with a brief high-current pulse — the standard method for building lithium packs, because soldering overheats cells.
Commercial Terms
- Bill of Materials (BOM) The itemised list of every component in a pack — the document that turns a price into something you can actually verify.
- Cell Traceability The records linking a finished pack's serial number back to the specific cell lots and test data that went into it.
- First Article Inspection (FAI) A documented check of the first unit off a production run against the agreed specification, before the rest of the batch is built.
- Incoterms (EXW / FOB / DDP) Standard trade terms defining where cost and risk transfer from seller to buyer — the reason two quotes are rarely comparable as printed.
- Injection Tooling The steel mould used to produce a plastic battery enclosure — usually the largest one-off cost in a custom pack program, and the slowest.
- Lead Time The interval between placing an order and receiving goods — composed of several stages that are frequently quoted as if they were one.
- Minimum Order Quantity (MOQ) The smallest order a supplier will accept for a given specification — driven by cell purchasing, setup, and certification cost rather than by policy.
- ODM (Original Design Manufacturer) A supplier that designs as well as builds the product, in contrast to an OEM arrangement where the buyer brings the design.
Still deciding on a specification?
Our longer guides cover the decisions these terms feed into — cell format, chemistry, voltage platform, and supplier selection.