Q: I have an iPhone 3GS and have 2 questions: First, when not in use does it harm the battery to keep the unit plugged in? Secondly, at night I turn it off completely; will this eventually damage the unit?
A: Under normal use, regularly keeping an iPod or iPhone plugged in to a power source will not do any harm. The charging circuit in these devices is designed to shut off when a full charge is reached, after which the device simply runs from the external power source.
The only issue here is that you should not always leave your iPod or iPhone connected to external power, since in this case, the battery is not getting used at all. Apple recommends that you run your device off battery power for a few hours at least once a month to ensure that the battery is actually getting used. For the majority of iPod and iPhone owners this is not going to be a problem at all.
You can find a much more in-depth explanation of iPod and iPhone battery life and charging questions in our May 9, 2008 Ask iLounge column.
To answer your second question, there is nothing wrong with shutting your iPhone off completely at night either and this will not harm your iPhone in any way. There’s no need to turn your iPhone completely off at night, but there’s also no harm in doing so.