Hi guys, A guy is offering to give me an iPhone 3s for free because the screen was broken and it wouldn't power on. I can fix the screen, but I'm not sure if I want to invest in it if I won't be able to power it on. I can replace the battery, but before I buy one, is there a way to tell if a new battery will fix it? Also, what's the diff between iPhone 3 and 3s? And should I make sure I have the right battery and/or screen when buying for this? or are they the same? Thanks!