I have removed and reseated the part the MagSafe connector, connects to (power module?). Issues before and after battery replacement have been somewhat intermittent in terms of power connector LED and CoconutBattery readings. Would like to remove the connector, but don't really have the equipment to do so, it is way smaller than the boards I used to rework for Seagate back in the early 90s. The motherboard is not dirty at all, it lives on my desk on a stand, except when on vacation, but thought I saw small bits of solder between legs on JTAG under microscope, used tweezers to clean. Watched Louis Rossmann video and cleaned out JTAG connector, booted normally, ONCE, after that, with full speed and good readings on CoconutBattery, (battery made in March 2020, 1 cycle). Displayed the battery as made in 1979 at that time. Thought maybe battery went bad even though it only had 3xx cycles, so bought iFixit kit and replaced the battery. Opened the back, unplugged battery, can boot with battery disconnected while plugged into power, but runs slow due to no battery. Plugged it back in on its stand the next day and nothing happened when I pressed the power button. I know the bag didn't get too hot because my candy bars didn't melt :-). It worked fine prior to vacation, never used it while away, schlepped it in computer bag, only removed from bag at airport security on the way there, and again on the way back.

Late 2015 macbook pro 13 logic board