Typically these types of drills are sold with a NiCAD battery. NiMh is basically a newer version of NiCaD which you can replace with because NiMh will usually have a higher capacity and therefore more runtime. If you have a local Batteries Plus Bulbs, they may be able to rebuild the battery and replace all of the cells. They still use NiCaD but they’ll have a higher capacity than OEM.