This Volstask battery pack contains ten 18650 2.0 Ah Lithium cells in two 5 cell welded banks.
Easily separated into two 5 cell packs and fits many 18 volt tools. 20volts --not really.
Great deal on the cells if you consider that are already welded together and worth it just for the cells.
I took it apart and used the cells to repair two of my drills.