No they are not totally interchangeable.
The KR808D-1 battery can use a DSE901 atomizer with no adapter
The DSE901 battery needs an adapter to provide the air inlets when to use KR808D-1 cartomizers. The DSE901 battery expects the air inlet to be in the DSE901 atomizer and does not provide the groove needed to direct air into the
threaded connection. That is why the adapter is needed.
There are also PCC incompatibilities. Some 901 PCCs will not charge KR8
batteries, some won't fit manual
batteries. The KR8 PCC with charge both KR8 and 901 autos and manuals as far as I know.