Please send a current copy of the page with your posts particularly if you aren't going to provide any information. I need some sort of information to formulate a post.
It looks like that isn't even the right recordset... I've opened up your page and your product details recordset is set to:
"SELECT * FROM Products WHERE ID = %s"
so that wasn't the issue in the first place.
It looks like the real issue is how you are trying to populate the productID hidden form element on line 436. You have:
<input type="hidden" name="eCart1_1_ID_Add" value="<?php echo((isset($_POST["BatchID"]))?$_POST["BatchID"]:"") ?>" >
but I don't think you are posting a BatchID to the page and I don't think it matches with a productID... I think it should probably be:
<input type="hidden" name="eCart1_1_ID_Add" value="<?php echo $row_ProductBatch['BatchID'];?>" >
I'm actually pretty lost with what you are trying to do on this page....
It actually seems like your Add to cart recordset should be the ProductBatch Recordset as well and all of the bindings should be updated to point to those columns.