13" MacBook Pro won't boot after battery replacement

Hello everyone, got a late 2013 13” macbook pro that refuses to turn on after replacing the battery.

Before the replacement, the battery life was always very faint. Although it would charge, it’d never hold its charge for long. The battery was replaced by a fellow tech of mine, and she said everything came on just fine when testing it after doing the replacement. I’m going to double check with her again to make sure she’s certain of this. However, the customer came in to pick it up and it just won’t boot.

Absolutely nothing comes on when I try to boot. Not the fan, any lights or the screen - nothing. It appears that the logic board just isn’t getting powered. When the charger is plugged in, it lights up red. I don’t know if the laptop is suppossed to turn on when plugged into a charger, but it doesn’t when I plug it in. I’m leaving the laptop plugged in over night, and I’ll check to see if it’s lit up green in the morning.

I’ve tried resetting the SMC, but no dice. Everything appears to be hooked up correctly after the replacement, but I can’t be certain until I run through a battery replacement again and check all the connections. I really trust my tech on this one, but I’m planning on tearing it down tomorrow morning to see for sure.

Is there particular connection that I should be looking for when tearing it down in the morning? Is there a chance that the logic board/battery isn’t getting power? Or maybe some other thing is at play here?

Any advice you guys may have would be greatly appreciated!