In most circumstances, unplugging your iPhone while it is still charging causes no problems. Unlike some older batteries, the iPhone battery does not suffer long-term effects from partial charges. You do need to take care when unplugging an iPhone from your computer, though.
Most misguided advice about charging batteries comes from the so-called memory effect. This affected older rechargeable batteries in a format called ni-cad and meant that repeatedly partially charging a battery would eventually reduce its total capacity. The iPhone uses a newer form of rechargeable battery known as lithium-ion. There's no hard evidence that lithium-ion batteries suffer from the memory effect and even the testing that suggests it suffer an effect does not suggest it is a significant problem for ordinary use.
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Apple does not issue any warning about unplugging a charger before a battery is completely charged. Apple specifically uses the term "charge cycle" in referring to battery life and notes that, for example, charging your iPhone battery to only increase charge by 25 percent counts as 25 percent of a charge cycle, confirming a complete charge is not needed every time. When using a wall charger, there is no requirement and no option to take any particular action or wait for a particular event before unplugging the charger.
Apple recommends carrying out a "complete charge cycle" once a month. This means draining the battery until it is completely empty and the phone automatically switches off, then charging it to full capacity. This is partly to keep the battery in good working order and partly to ensure the remaining battery charge indicator on the phone display remains accurate.
Apple's charge indicator display has caused confusion, with the display showing 100 percent while the phone continues to charge. In March 2012, Apple explained that this is because its devices do not simply hit full capacity and then stop charging. Instead they hit full capacity, drain a little, charge up to full capacity again, drain a little, and so on. This cycle prevents damage if the phone is left connected to a charger even after charging is complete. The Apple display shows 100 percent when the device begins this cycle and continues to display 100 percent throughout the cycle. Apple insists that you will get at least the full advertised battery life whenever the display shows 100 percent.
If your iPhone is connected to your computer for charging and you have iTunes open, the iPhone displays as a connected device both while syncing and beyond. Apple recommends that in this situation you "eject" the iPhone on the computer before physically unplugging it. To do so, wait until syncing is complete; then click the upward arrow icon next to the name assigned to your iPhone and click on "Eject." This is mainly a safeguard to prevent you accidentally unplugging during a sync or software upgrade, which could cause problems.