To answer your question on batteries there are a few basic things you need to know
MAH = capacity or the size of your fuel tank so to speak, the higher the number the larger the fuel tank or run time.
Number of cell = Nimh/nicd cells are 1.2 volts each and LiPo cells are 3.7 volts each,this determines how fast a motor will spin, the more cells the faster it will turn, most people run between 6 & 14 cells Nimh/nicd or 2 & 6 cells LiPo depending on the type of vehicle/motor/ESC you are running.
Then there is the Charger = The type of charger you need depends on the type of batteries you choose to run, if you plan on running electric for a while do you self a favor and invest in a decent AC/DC charger that will charge both types of batteries, like hyperion, as fas as charging you batteries goes the general rule of thumb is to charge them at 0.1amp per 100mah, so if if you had say a 5000mah battery you could charge it at 5 amps and it would take about an hour to charge.
So in your case a few quality 8 cell 5000mah batteries would give you some good long run times and speed.
www.cheapbatterypacks.com has 5000mah elite 8 cell packs with 14 gage wire and a traxxas plug for $50 each.
http://www.cheapbatterypacks.com/main.asp
ummm like the 3000mAh NiMH 7.2V 6-cell stick pack that it comes with it off tower hobbies
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXXMY8**&P=FR
That battery would work but it will not last as long or give you the speed or run time that the battery I suggested for you.
