Sounds like you'll need ten 1.2 volt, 2000mAh, Nickle Cadmium Metal Hydride battery cells connected to each other in series. If you have some leeway with how many volts you need, you could try a 3 cell, 11.1 volt or 4 cell, 14.8 volt, 2000mAh Lithium Polymer battery pack as well. If you're limited in how much space you have, I'd look at Li-Po's made for "park flier" type RC aircraft since they're small and light when compared to Ni-Cd's and Ni-MH packs, especially at that voltage!
BTW, 2000mAh is 2 amps, 1 amp hour in storage is the equivalent to 1000 Milli amp hours in storage if anybody doesn't already know that