Macbook Pro 15" Retina Mid 2012 Battery and I/O Board replacement
Il Mio Problema
My battery had the 'Service Now' indicator and my HDMI port hasn't worked for about a year. Time to fix it!
La Mia Riparazione
Really well, apart from being a bit nerve wracking prying the battery out.
Il Mio Consiglio
Replacing the battery:
1. put the laptop face down on the edge of a table with the screen open (angled so the screen sits off the table). Put a towel under the laptop folded in such a way to make the battery the lowest point. This is to stop excess IPA going into the motherboard area and also to prevent any IPA from seeping into the screen (through the trackpad).
2. You need to leave the Iso propyl alcohol in for a long time, and you need a lot of it (I used about 200-300ml)
3. Start prying the outer two cells first. Once you've got them up there's a metal plate that the middle cells are glued to that lifts up so you can do that removal out of the computer.
Don't remove the fan cable (which is very firmly glued down - thus risking breaking it), just fold the fan over.