Funny story.
I ran the battery down on my Quantum while it was plugged in. I was watching Netflix. I did not get a battery warning or anything, just boom, device off. I thought, no big deal, just let it charge back up. 24 hours later - nothing. It just did not seem to be taking a charge. I call AT&T to file a warrenty claim. They handled that just fine, but the tech support guy told me that I should not be using the phone when it is plugged in and that they in fact recommend that it be turned off when charging. I asked him if he knew much about windows phones and he said that he was in fact a high level technical support person for windows phones. I said that I doubted that.