I can say that from personal experience, it hurts the battery. I just bought a 4th gen off my friend and she kept it plugged in basically 24/7. now, the battery is very messed up. If you use wifi it'll kill it within 20 minutes. Then itll boot right back up if you turn it on, but itll say it has like half a battery! I figured that maybe if i drain it completely, it might fix the issue, so i kept killing it and rebooting it till the very low battery screen kept coming on. So, i plugged it in, ans when it booted up, it said it was halfway charged! And it doesnt like the cold eiither. if it gets a lil cold, itll glitch out and not turn back on till you plug it in. If you dont use wifi or play games (basically just listening to music), it lasts an OK amount of time. Even in standby mode, itll lose power. I hope a restore will fix it, but if not, the battery is fried. 😡