6 d-cells means it's a 9v power system which is pretty strong, but D-cells also carry quite a lot of energy in them, that's why they're so big. I would think 6 Ds means hours of firing time.
Regardless of the features and whatever magazines might be included, I don't think I'll be getting it. I didn't realize the Vulcan uses the same amount of batteries but given that it generally rests on a tripod and isn't trying to be the practical weapon, meaning you'll only bring it out every so often, justifies the battery requirements somewhat.
For a rifle you'll probably want to regularly use, though? Unless the motor works off of a minute amount of power and the batteries will last a long freaking time, it's really difficult to get excited about dealing with that. I think my next Nerf purchase will continue to wait until I (hopefully) find the Raider available again with a second drum mag included.