DM18RL Battery Adapter for Ryobi 18V Power Tools, Adaptor Convert for Dewalt & for Milwaukee M18 Convert for Ryobi 18V Power Tools: Amazon.co.uk: DIY & Tools
DeWalt to Ryobi 18-20V Battery Adapter – Badaptor
Badaptor - DeWalt to Ryobi 18-20V battery adapter | eBay