Design and function: Cycling
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Cycling means all the discharging and charging in a battery. A battery is always cycling. Discharging, or cycling, can have varying degrees of depth. Deeper discharge is more damaging than lesser discharge. Each discharge results in stress to the plates which deteriorate accordingly. Each instance of cycling cause the material in the plates to become more fragile and ultimately some of this material will separate from the plates. Cycling results in a reduction of capacity.
A lead battery cannot tolerate infinite cycling. Deep discharges should be avoided in order to maintain as long a service life as possible.