I just replaced my iMac with a 15" MacBook Pro. I work from home on a windows laptop and on my desk was my iMac which I used the headphone output to a seperates system amp so I could listen to my music while I work. I would like to do the same now but am unsure if this will be too much on the battery, or if there is a best practice for this. Would keeping it plugged in while it is being used shorten the battery life... should I use it unplugged until I reach a certain level and then plug it in. I am just wondering this as it will be using iTunes almost all day but not actually in proper use by me. Hope that makes sense!