I've been noticing several vendors are getting away from using the 4D/8D and Group terms. Mastervolt is a good example - they don't even reference this info on their product pages. In addition, new battery types/sizes are coming out. We selected, because of space issues and wanting to maximize the AH availability for the space we had, the Mastervolt slimline AGM batteries. While still weighing 120lbs or so, they are much skinnier and easier to deal with moving around. We can fit almost 400AH of capacity in the same space as a traditional 8D. You can get more info on our particular battery here - http://bit.ly/j2MaZA. The new Mastervolt Lithium Ion batteries also are also smaller than an 8D, but at close to $7k for 320AH they need to come down a bit in price