Why any battery is not recognized?

Hello,

I have a MacBook Pro unibody mid 2010 for service.

The problem is the laptop didnt charge at all when they first came in.

We changed the battery and did exactly the same thing.

We then changed the battery plug cable and when you power up the computer you can see the orange light, the system starts and you see the battery icon showing 0% and a lightning, showing that the battery is charging. After a few minutes those dissapear and you can see an X over the battery and the battery is not recognized anymore.

We found some water damage and decided to change the whole mother-board. We bought exactly the same mother board for this model, of course with another serial no. and is doing exactly the same thing but the new problem is we can't see the serial no. in about this Mac.

We need some help please.

We dont know what to change or what to reset further on.

Thank you!