Galaxy S6 not charging/turning on

I'm a newb who recently just got into phone repairs, since starting I've done about 3 Apple phones (had to send 1 phone out for a logic board repair as I was in way over my head), and resold them.

Anyway, got this S6 for next to nothing so I thought I would make it my first Samsung repair. It was described as not turning on, back cover cracked. My thoughts turned to battery and charging port, and the parts were cheap enough so I just bought the parts for a swap instead of checking them. It's been a good experience doing the swap except I accidentally cracked the LCD while taking the display assembly off. That's fine, got the phone for nothing. The battery/charging port replacement seemed to work, now when I plug the charger in it will vibrate once and the red light flashes (did not do that with the old charging port/battery). It seemed to be the battery, but didn't check the charging port, because I tested the new charging port with the old and new battery.

I reassembled everything except for the back glass, and left it charging all night. The phone still won't turn on.

Anyone have any ideas, I don't want to get an LCD replacement if its not the problem as I'd be out $250.