Cycle Life
The number of discharge-charge cycles a battery can complete before its capacity falls below a defined threshold. It is not a fixed number; it depends on depth of discharge, temperature and charge profile. In lead-acid at 50% depth of discharge, typically 500–1000 cycles are expected.
Cycle life only makes sense when stated together with a depth of discharge. The same battery gives typically 500–1000 cycles at 50% DoD, while that number roughly halves if it is discharged 80% every time. Manufacturer catalogues usually present this relationship as a logarithmic curve.
Temperature is the second major factor. In lead-acid batteries a high ambient temperature accelerates chemical ageing; a low temperature reduces the instantaneous capacity. The accuracy of the charge profile is decisive as well: persistent undercharging produces sulphation, while persistent overcharging produces water loss and plate corrosion.
For an RV owner the practical measure is this: if you camp 100 nights a year and use one cycle each night, a lead-acid bank kept at 50% DoD typically serves for something like five years. If you do the same usage at 80% DoD, the same battery is replaced much sooner. Drawing the levelling, lighting and pump load from a correctly sized battery bank is therefore decisive in the long run.
Context in which this term is used: RV automatic levelling guide