The Adaptor enables you to connect new powerfull 
18 V – 20 V slide batteries with a range of old DeWALT XRP powertools. Save money, do the environment a favour, and get more out of your existing machines!
The adapter fits most XRP machines, but a few machines require a minor modification. For instance the Nail gun, the Circular saw and a few others, you can also checkout how to modify the machines by watching our video. The modification will be shown at 2:15 in the video shown below.
The first series of adaptors that were introduced to the market did not have a built-in overload protection. Therefore, the series was withdrawn and new secured adapters came on the market. 

On the left is a picture of the first series ( right) 
and the new secured series (left). The video below also shows how the adapter is protected against short circuits even in extreme cases.

The Manual for Adaptor is linked here:  Manual A-Link adaptor for DeWALT powertool