Discharge Curve

What the shape tells you

Plot voltage on the vertical axis and energy drawn on the horizontal, and you get the curve that governs how the pack behaves in service.

A lithium NMC pack drops quickly at the start, then settles into a long, gently sloping plateau across most of the usable range, then falls away sharply at the end. The plateau is why the pack delivers consistent power for most of a ride, and the sharp tail is why the last few percent disappear quickly.

The curve moves with conditions: higher current pulls the whole curve down through voltage sag, and cold does the same.

Why chemistry choice shows up here

LiFePO4 has a notably flatter plateau than NMC. That is good for delivering steady power and bad for voltage-based fuel gauging — if voltage barely changes between 70% and 30% full, a gauge reading voltage alone cannot distinguish them.

This is a concrete, often-overlooked consequence of the NMC versus LiFePO4 decision: choosing the flatter chemistry effectively obliges you to use coulomb counting or a combined method for state of charge, rather than a cheap voltage lookup.

Why it matters for replacement packs

A replacement battery has to match more than voltage and capacity. The original bike’s display was calibrated against the original pack’s curve. Fit a pack with a different curve and the gauge misreads — not because either component is faulty, but because the display’s lookup table no longer describes the battery it is reading.

This is why we ask for a sample unit where possible. Profiling the original discharge curve, and matching BMS cutoff behaviour to it, is what makes a replacement behave like the battery it replaces rather than merely fit the same bracket.

If your display reads voltage, say so

If your display infers charge from voltage, tell us — the curve becomes a design constraint rather than a by-product. If it reads over UART or CAN, the curve matters much less, because the pack reports its own state instead of being guessed at.