Difference between the different DeWalt batteries (20v max) 18v Li-Ion and 36v?

I’m thinking of selling my old tools and getting new ones and I was wondering what the difference in power and capacity it is between the above batteries and I’m only talking about the 3 or 4ah 20v batteries. The smaller don’t interest me.

I also have a circular saw in 36v and plenty of 18v tools and I have both XRP packs and a couple of Li-Ion 18v packs.

Also, is dewalt coming out with higher voltage tools such as a new line of 30-36v or something (Lithium)?

Thanks

George