Lithium Iron , Nickel Metal Hydride or Ni-Cad.
What Cordless Tool battery?
The very latest Li-ion type of cordless batteries will give the best performance. Next in line will be the Ni Met Hydride type and then bringing up the rear are the good old Ni-Cad batteries.
The trouble with the old fashioned Ni-Cad batteries was that they tended to develop a memory. What this meant was that if you decided to recharge your battery when it was only half discharged, then it would tend to give you only half as much time of usage.
The later Ni-Met-Hydride ones were much better as they had got rid of the memory factor. The characteristics of these were that the power got less and less as the battery discharged.
The latest type are the Lithium Iron type which i use in my tools. These are great as they seem to give you loads of power right up until the moment they become exhausted. There are some great cordless drills around now such as the Milwaukee 18V range with batteries from 1.5 ampHr up to 3.0 ampHr. I use these daily and find them very touch tools indeed .Buy one off me and see!
Hitachi has just brought out a 4.0 ampHr battery for their 18V range of power tools. These should last ages as well.