I just went through this process and am appreciative of the guides. I say ‘guides’ (plural) because there are a number of 30-some step procedures for the similar models of Macbook Pro, and they all contain about 25 steps too many. Like many of the others, I did steps 1-4 then carefully freed my discharged battery using a plastic smudger. New one installed without a hitch and my trackpad, which was previously not working properly due to pressure from a swollen battery, is now back to functioning perfectly. Definitely worth the work to get another 2-4 years out of this laptop.
Pro tip: use ‘yes’ to blast your CPU and empty your old battery quickly. In terminal run ‘yes /dev/null’ for each CPU you want to stress so for 4 CPUs you’d do:
yes > /dev/null & yes > /dev/null & yes > /dev/null & yes > /dev/null
If you command-c to quit you’ll only kill one, oddly so after exiting out you’ll need to do this to kill the rest:
killall -HUP yes