I found that you don't need to disconnect the battery... why bother doing more fiddling with annoyingly tiny screws and obstinate cable connectors when you don't actually have to? Especially when you could only end up causing more damage. As a matter of fact, the original iFixit video didn't bother to disconnect the battery either, but they've since updated the video to include battery disconnection, I guess as a "belt and braces" approach in case the repair-hero forgets to power down the phone first?