Cycle life refers to how many complete charges and discharges a rechargeable battery can undergo before it will no longer hold a charge. A charging cycle is completed when a battery goes from completely charged to completely discharged. Therefore, discharging a battery to 50% and then charging it back up to 100% would only be counted as 1/2 of a single battery cycle.
Battery cycles are used as an estimate of what a battery’s overall lifespan will be. If you have a sealed lead acid (SLA) battery with a lifespan of 500 cycles, you can reasonably expect it to last 500 complete charging cycles. Keep in mind that the estimated number of charging cycles does not always indicate how long a battery will last since there are other factors at work, including what temperatures the battery is exposed to and how well it is maintained.
Capacity drops as part of cycling
More information on battery cycle life here
Did you know?….
You can make a battery out of potatoes; it’s not strong enough to power a LED flashlight though