I did it last year on my 2012 rMBpro after it have been complaining about servicing the battery for about a year, and while it wasn't a walk in the park, it all worked out great.
Tip: there are 2 ways to replace the battery.
One is by following the official iFixit etc instructions where you remove absolutely everything before you peel off the battery with acetone.
The other is by immediately peeling off the battery right away. In that case, you have to be careful that the acetone doesn't flow onto the speakers (because they'd melt.) That's the way I, and many other with me, did it. It still only took me about 1 hour to get everything back up and running.
They did say that they might need to replace the shell (battery was slightly swollen in both machines) and that I'd be responsible for that cost, but that didn't happen for either box. I don't think they replace the shell unless it's really, really deformed. Neither of my machines would sit flat and both were obviously swollen. One I could practically spin like a top (and the trackpad was screwed).
I got both back with no deformities, a new battery, keyboard, and trackpad, and a 199 bill (plus tax).
I wouldn't rule out getting it fixed. If you do end up paying a little more, then you can probably sell it for more than the price it cost to fix.
Last time I looked I was quoted somewhere in the neighbourhood of $600 for a rMBP battery replacement - but that was just the battery. Even that IMO is not a reasonable cost for what it is - the only reason it costs that much is the fact that it's glued in, and the fact that Apple charge so much for the part.
Replacing a Macbook battery should be a routine task for any of them.
You can also replace the thermal paste, although now that it's not overheating all the time, I won't have that done until next time it overheats and slows down and I need to have it vacuumed out again.
http://www.mackungfu.org/TheonethingtodotomakeyourMacBookPro...
i bought an $80 battery (ifixit? i can't remember now) and took it to a local shop and had it back in 3 hours. they charged $120. So... ~$200 but I had same day replacement.
* Advice from the internet: procede with caution.
Do you mean "not having anything other than USB C is lame", or "I dislike USB C and wished Apple had gone with something else"?
I really don't care about the "charge from either side" benefit of USB Type C. I do appreciate the fact that you can use aftermarket cables though - especially considering how poorly constructed Apple's are.
What do you dislike about the OS? Presumably it's running macOS Mojave?
I am sure I will think of some other annoyances. I've kept a 2012 MBP on Sierra, and love that machine far more, eg. keyboard is actually good and is quiet, real function keys, real ports as found on every other device in the universe, ability to use my audio interface, network ports etc etc
http://osxdaily.com/2018/10/15/dark-menu-dock-light-theme-ma...
Edit. It does to a degree. Firefox takes on the dark theme but everything else seems fine so far.
Have tried everything short of a complete reformat - NVRAM, SMC reset. Nothing in activity monitor gives me any clues either.
I even rolled back to High Sierra to check my sanity. No crazy fan spin. Reinstalled Mojave --> crazy fan spin.
Unfortunately it's not at all normal, it's swollen to the extent that the bottom of the case is slightly warped and the macbook will no longer sit flat. It's also affected the trackpad which doesn't click very well any more. I noticed these things a while back but didn't realise that the battery was the cause until I opened it up a couple of days ago to clean it out (something I do once or twice a year).
Now awaiting a battery replacement kit from iFixit and not looking forward to removing the old one. Probably going to try the dental floss method someone mentioned above (very, very carefully and far away from anything flammable).