If you charge your cell phone while it's on, does it take longer to fully charge?

I always thought it was because your phone obviously needs energy to light up the screen and receive/send any texts or calls. But my mom and a friend of mine insist it’ll take the same time, on or not. Didn’t make much sense to me. So which is it?

I would think it depends on the cell phone and the charger. I know my iPhone takes longer to charge off of USB than it does off of the wall charger. If the charger for your particular phone is not capable of giving the batteries a maximum charge current AND running the phone at the same time, then it will take longer.

Ah, I see.
And you have an iPhone…I am so jealous. My phone has an mp3 player but it only holds about 100 songs. Which is pathetic for a music whore like me.

It was a birthday present (and possibly all future birthday presents forever…).
BTW, if you are REALLY interested in this problem, just do a timed test.

I’m with beowulff. There’s more juice available from a wall outlet than is needed to charge your phone and operate it simultaneously. It comes down to whether or not the charger is capable of taking advantage of all that juice.

Check your manual, and if you don’t believe what it says, try to force your phone to remain on and operating in some way (backlight or a long weekend phonecall) and see if you notice a difference.

Provided the charger can handle the additional current needed when the device is on, and most should, the time needed to charge the battery with the device on will be the same.

Actually it might take longer to charge with it running. And it might could end up hurting your battery too.

The phones today create a fair amount of heat from their processor and high-speed data transfer (I know my Samsung Blackjack can get especially warm when it’s tagged to a 3G network, as opposed of GSM), and excess heat is not good when you are charging batteries. Charging a hot battery is a good way to kill the cells prematurely.

I don’t know if cell phone batteries have protection from heat but I know some of the more advanced two-way radio chargers I sell will not charge a hot battery until it has cooled off.

Because the battery is hot or because the resistance is higher?

There will be a difference in current drawn between On and In Use.