Batch Name for all journals in NAV is "collective name" for the group of journals. It is not clear to me, why you want to use Batch Name for WIP? We usually use material quantity in 'WIP', but no output quantity in WIP.
You have report Inventory Valuation WIP, but this is not expected output quantity. This report present Consumption, Capacity and Output costs.
Expected output quantity is on PO header. Can you describe reasons precisely?