Charles:
1) I presume you mean FOUR nimh AAs per set (the d7 needs 4 batteries to run)
2) AD 20 MAY work for a set with the nicd 9v batteries, but, unlike the aa batteries, the 9v nicd (or nimh) batteries hold a fair amount LESS juice than their alkaline counterparts. BE SURE to make a few test runs on the ad20 using the 9v nicd batteries before you go out into the field to be sure you know how long they will last powering the ad20. If you need more run time on the ad20, the best solution is to rig up an external battery pack.