It counts full charge and discharge cycles to a stated depth, after which the pack still holds a stated percentage of its original capacity. Without both of those qualifiers the number compares to nothing, and the two are frequently omitted from listings.
Cycle life is the specification that most rewards reading the small print, because the headline figure is set by assumptions rather than by the cells.
The two qualifiers
Depth of discharge: how far down the test took the pack on each cycle. End-of-life capacity: what fraction of the original the pack must still hold when the count is reached. Change either assumption and the same cells produce a very different headline.
Why the same pack has several ratings
Makers frequently publish more than one figure — a larger count at a shallower depth, a smaller one at full depth — and both are honest. A listing quoting only the largest is selecting rather than lying, which is why the product page on this site reports the qualifiers wherever they are published.
What ages a pack besides cycling
Calendar age, temperature and the state of charge it spends its life at. A pack that sits full and warm ages even if it is never used, and this is not counted anywhere in a cycle rating.
What to compare instead
Usable energy across the expected life, which is cycles multiplied by usable capacity, read with the qualifiers attached. It is a more awkward number than the headline, and it is the one that corresponds to what the battery will actually deliver.
What people ask before they order
Does a partial discharge count as a cycle?
Not as a whole one. Cycles are conventionally counted as accumulated throughput, so several shallow discharges add up to one full cycle — which is why shallow cycling extends calendar life.
Does a battery stop working at the end of its rating?
No. The rating marks the point where capacity has fallen to the stated percentage. The pack continues, holding less, and the decline continues with it.
Last reviewed 16 September 2026