Used this guide to replace my stock Hitachi HDD with an Intel SSD. I also figured I would replace the battery while I had the case open, it had almost 700 charge cycles and about 70% capacity remaining. My MBP has been running like hot garbage, literally. The fans would spin up and it would get dangerously hot near the upper left of the keyboard just doing mundane tasks like web browsing. It would chug along and I’d get the beach ball constantly. I decided to reset the SMC while I had the battery out as well out just to be safe. After the repairs were done my laptop booted up perfectly on the first try and it’s running like new again. Great guide and I hope this comment helps anybody having the same issues as I was.