The new batteries are unlikely to make a significant difference. I purchased a CSX 18 Skin as I already had two 3.1Ah 18v batteries for use in a 18/4. The reason for the 3.1 batteries in a large drill was to make it as light as possible. Having two batteries meant that there was always one charged in reserve. With teh CSX 18, I decided to get two more batteries, again the smallest I could find, which were the 3.0Ah. Now the point is that the external design of the batteries does not change. And, frankly, these batteries should last 10 years. Then they will be re-packed or replaced. Each has enough charge to last at least a month of use. More charge is not going to give me more use from the drill. A newer technology sounds good but a lower price makes an older battery a better deal.
Regards from Perth
Derek