Help! Don’t know where this black cover goes on my Prius battery!

I have a battery rack trays and all that apart right now I just broke down 56 cells I think I'll have to go out and look for that piece or else it's in the car

 

I've disassembled probably a hundred Gen 3 HV batteries. I don't recall that component being on any of them. I would venture to say it belongs to something external to the HV battery.

Very often, these items have a Toyota part number molded into the plastic in an 'out of view' location. If it does, Google has always provided the answer for me.

Oops, just re-read the post and you've apparently found a part number already. Can you post that?
It almost looks to be a piece to cover openings in ducts or something similar. Where was it located when you found it?

 

Deleted

 

A ruler or tape measure in the pic would help. Luckily you have a bit of finger in one pic, gives some sense of scale.

 

One thing we can say from that is it isn't a Toyota part number, because Toyota part numbers look like nnnnn-nnnnn.

But that's not any worse luck than usual, because even a lot of the times when a Toyota part has an nnnnn-nnnnn number stamped on it, that number isn't the part number either.