Where can I get a battery for my Performance (B&Q) Drill?

My latest portable Performance Drill, 18v. EAN No. 05019175, battery packed in. Opening it up I discovered so much corrosion that a repair would be impossible. The number the local B&Q provided, the same on the drill - 0845 300 2577 no longer responds. It seems a shame to consign the unit and its large charger to the recycling bin if a battery is available.
Any ideas?