How Will Leaving Your iPhone Plugged in Affect Battery Life?

The iPhone’s lithium-ion polymer battery differs significantly from the nickel-based batteries that power many electronic devices. It's lighter, smaller, more durable and more environmentally friendly. It's also more efficient. It doesn't suffer memory effect, which requires nickel-cadmium batteries to completely drain of power before recharging to achieve a 100 percent charge. When plugged in, it charges rapidly to 80 percent, trickle-charges over the last 20 percent and then stops charging when full. Hence, you can subject your iPhone battery to frequent, shallow charges or leave it plugged into power without fear of degrading or overcharging it.

Technically, battery life refers to the time between charges. When your iPhone is plugged into power, you enjoy prolonged battery life. Your device will have enough juice to serve your every need -- such as a bright touch screen set to never sleep, all wireless radios working furiously behind the scenes while you watch a movie, playing a 3-D game or listening to music in enhanced modes -- regardless of whether the usual power-hogging suspects are at play.

Power is to your iPhone battery as sweets are to a human: It has the potential of inflicting too much of a good thing. Keeping your iPhone plugged into power can shorten its battery’s life span, or the amount of time before you must replace it. You actually strengthen your lithium-ion battery and prevent its premature demise each time you make it power your iPhone on its own, without the crutch of a power source. As Apple puts it, “It’s important to keep the electrons in it moving occasionally.”

Charge cycle your battery at least once a month if you tend to leave your iPhone plugged into a power source. Cycling involves charging the battery to 100 percent and then draining it completely until the iPhone shuts down. As you wean your device off of an external power source, your charge cycles happen organically and cumulatively with use. For instance, you would complete one charge cycle in four days if you used up your iPhone battery 25 percent and recharged it to 100 percent each day. You can expect your iPhone battery to complete 400 charge cycles before it drops to 80 percent of its capacity.