Capacity Fade

Permanent loss, not temporary

Two things reduce the range a rider gets, and conflating them causes bad warranty decisions.

Temporary reductions come from cold weather, high current draw, or voltage sag. The capacity returns when conditions normalise.

Capacity fade does not come back. It is physical change inside the cell — growth of the solid-electrolyte interphase layer, loss of cyclable lithium, gradual rise in internal resistance.

A customer complaining in January about lost range usually has a temperature problem. The same customer complaining in June, three years in, has fade.

Calendar ageing and cycle ageing

Fade accrues on two independent clocks, and buyers routinely account for only one.

Cycle ageing tracks use, and is what cycle life figures measure. It is driven by throughput, depth of discharge, charge rate, and temperature during cycling.

Calendar ageing happens regardless of use. A pack sitting in a warehouse ages, and it ages faster when stored hot and at high charge. This is why unsold inventory is a depreciating asset in a way that non-electronic stock is not, and why a pack manufactured two years before it is sold does not start life at 100%.

Managing it

In specification: oversize capacity so the pack still meets the requirement at 80% state of health, not just when new. A pack that exactly meets the range target on day one fails it within two years by design.

In storage: cool and at partial charge. Warehouse temperature is a real lever — it drives self-discharge as well as calendar ageing, so a hot warehouse costs you charge and capacity at the same time.

In the warranty: define the threshold. A warranty that promises the battery will “hold its capacity” invites disputes; one that specifies a percentage retained after a stated number of cycles or months is enforceable in both directions.

In the field: for fleets, measured capacity beats calendar age as a replacement trigger — packs in identical service fade at noticeably different rates.