The Dewalt DC9181 Batteries are 1.1Ah Sony Lithium Iron Phosphate batteries. The Dewalt DC9180 are 2.2Ah A123 Nano Phosphate Lithium Ion.
Differences are runtime, cycle life, weight, and power density.
DC9181 was designed for those who readily have a charger available, and place a higher importance on weight and ergonomics. It's not suitable for XRP tools, even thought they will work in them. You will see slightly less power, and less runtime.
The DC9180 was designed for people who wanted a good balance between weight and runtime. It's got twice the runtime and twice the cycle life over the DC9180.
If you choose to buy the DCD970 as a bare tool, I would not recommend using the DC9181 batteries with it. When you start buying that many bare tools, it's worth it to just buy the kit. You will save money that way.
Ok thanks!! It actually makes sense to git the kit as I was looking on ebay earlier and just the bare DC970 goes for around $110-$120 shipped and I can get the kit with the DC970 hammer drill, DC9130 charger and 2 DC9180 XPR batts from around $250-$290. Now I have another question eventually I would like to get that hammer drill (DC970KL kit) but first I will be getting the DC390 circular saw and the DC385 recip saw both bare tools and will use my DC9181 batts that came with the DCD265L kit I just got. Will the DC9181 batts work fine with the circular saw and the recip saw? If not like I said eventually I will be getting the hammer drill which comes with 2 DC9180 XRP batts that I can use on the saws.
