ARE YOU SURE YOUR SMC RESET ACTUALLY HAPPENED?? HOW TO KNOW: I installed iFixit kit new battery 3mo ago into my mid-2012 MBP Retina with success except for a very abnormal battery discharge pattern (dropped to 77% in 1h, then to 28% in next 15min, then to auto-shutdown in next 45m). After multiple recalibrations, and after multiple attempts to reset SMC using the iFixit link to Apple instructions, nothing changed.

This week I discovered that the Apple instructions are correct but incomplete. Here’s what finally worked for me and gives confirmation that SMC reset occurred and for me restored normal battery discharge behavior: With battery down to about 10%, shut down Mac with lid still open; connect the charging cord; do the Apple-prescribed left-side SHIFT-CONTROL-OPTION , plus POWER key; hold for ≥10 sec; release all 4 together AND WATCH THE MAG-SAFE LED CONFIRM SMC RESET BY BRIEFLY TURNING GREEN AND THEN BACK TO RED. (Not sure if 10% state of charge is needed — might just need the red charging LED.)