Battery degradation

Battery degradation is the gradual decline of the usable capacity of a drive battery through ageing (calendar degradation — the battery ages even when barely used) and use (cyclic degradation — each charge cycle wears the battery slightly). The visible result is a slowly shrinking range. The course is non-linear: often a somewhat faster drop in the first year, then a flatter line.

Fleet data and owner reports point roughly to a few percent capacity loss per year under normal use, with a large spread. A lot of fast charging, routinely charging to 100 percent, standing full or empty for long periods and high temperatures speed it up; moderate charging behaviour slows it. Figures are indicative and depend on chemistry, thermal management and use; for newer battery types the data series is short.

Degradation is something other than a defect: see the battery warranty, which usually guarantees a capacity threshold (often around 70 percent) over a term. Normal degradation above that threshold usually falls outside warranty. We show degradation pictures only with source and reference date and only with enough data.