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The battery’s cycle life is an important term used to describe deep-cycle batteries.
One battery cycle involves discharging the battery by a certain amount and then recharging it to full the amount.
The battery’s cycle life is the number of charges and discharges that a battery can complete before losing performance.
What Affects the Battery’s Cycle Life?
Depth of Discharge
The amount you discharge a battery is called depth of discharge (DoD).
For example, if you have a 100 amp-hour battery and you use only 20 amp-hours, you discharged your battery 20%. This means your depth of discharge is 20% (and your state of charge or SOC is 80%).
As a general rule, the less you drain from your battery each time before charging it, the longer it will last.
If you have a lithium battery and you occasionally discharge the battery 100%, it doesn’t mean that you will be stuck with an inefficient battery. However, discharging a battery too much too often (beyond 80% DOD) does reduce the life of the battery.
On the other hand, most lead-acid batteries experience significantly reduced cycle life if they are discharged below 50%.
If you discharge and charge a battery in an environment with a mild temperature, you can expect to get more cycles out of the battery than if it was in a very cold or hot environment.
(If you live in a cold climate, you might be interested in reading my post: Do Lithium Batteries Work in Cold Weather?)
Charge & Discharge Duration
If you charge or discharge a battery too quickly, you will decrease the cycle life of a battery.
The good news is that most solar systems that people use today will typically have the battery charge and discharge slowly, so chances are you really don’t have to worry about this.
Unfortunately, a battery will deteriorate with time and eventually stop storing electricity. This will even happen if a battery is left alone, in storage.