Diag. code PPT004 after battery replacement, conditioning, SMC reset

Teenager presents me with their laptop, A1398 EMC 2674, says battery always displays as 0% charged, orange light on power cord, cannot unplug or computer loses power. I replace the battery with an iFixit model, second time going through that process overall (first time for this laptop), no difficulties. I conditioned the battery per iFixit’s battery calibration business card included in the order. Post-conditioning diagnostics report PPT004 (unfortunately, I did not run diagnostics before replacing the battery). I find some posts here and elsewhere suggesting PPT004 is Apple fearmongering. I put the battery through another drain/charge cycle, reset SMC and PRAM. PPT004 still reported. I remove the bottom panel, disconnect battery, inspect circuit boards. Find some grunge on the magsafe connector board, but it comes right off with some isopropyl alcohol, wipe has a slight yellowish tint, so I suspect old flux. I drain/charge the battery again, reset SMC and PRAM again, but code remains. Still have original Apple battery if needed to take to repair, but would really like not to go to those lengths. Any suggestions? Thanks, David

Top of magsafe connector before cleaning

Underside of magsafe connector in case that is useful