Only starts if I first disconnect battery for a few seconds

I have a mid 2011 MacBook Pro which shows green light on mag, but will only boot if I disconnect the battery for a few seconds. I tried 2 different batteries, both show over 95% design capacity. The laptop boots with just mag power after a few seconds without battery. I have continuously unplug the battery to get it to start. However, restart seems to work OK. Baffling...yes it is the dreaded 820-2915 but this is not kernel panicking…yet. Actually was able to run “Heaven “on it, so GPU seems fine for now.