What are "battery cycles"?

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Apple uses the battery cycle count to determine the battery health, the higher the number the weaker the battery.

So even though your battery has no physical damages you may find that it is not charging or holding its charge as well as before.

Obviously your battery will need to be replaced if it is swollen or other physical damage regardless of what the battery status says.

You can find your battery cycle by clicking on the apple logo on the top left corner of your screen, select About This Mac, click on System Report and select Power on the right menu.