Antonyh. Welcome to the Board.
The problem you face is a very common one. Lots of obsolete (dead) stock that no one will write off.
A simple calculation of the cost of this dead stock can be quite easy.
How much space is occupied by the dead stock? Either square feet or cubic feet.
What % of the total warehouse space is this?
What is the total fixed cost of the warehouse? Lease/rent or if owned an imputed rental (ie a market rental, because owning the warehouse actually costs you money)
Also include in the warehouse fixed costs, anything related to maintaining the building, security etc. Any costs that are incurred, even if the stock does not move.
So whatever the total fixed cost, take the % of that occupied by the dead stock.
Cost of Capital
To own the stock involves tying up capital. Capital costs you money. Typically 7% at today's interest rates.
So 7% of the value of the stock now is added as an annual cost.
Even if the stock is not moving, you need to maintain it, count it and so on.
That takes some labour cost. So include that.
So add up all the costs of holding this dead stock.
On the flip side, you can at least recover some money if you sell it.
And you will ceate free space in the warehouse to hold stock that does sell.
That was just a quick back of the envelope approach, but I hope it helps.