4 AA just about fit in a D space. But in a Mag, where tolerances are very close, there are actually some brands of batteries and some capacities of rechargeable AA that are just that little bit too big to fit. It is a very close call as to whether it will fit. Of course you could always get your Mag bored out a little, or select cells that will fit.
The other thing, as pointed out by PaulR, is that the Aventrade stuff hooks up the AA cells in parallel for 1.5V output. You will have to figure out a way to wire them up in series (which is possible but difficult because of the tight space restrictions) if you want to use it with the DB.