For details on LiPo batteries, visit the LiPo Page.
When building a Car or Truck from a kit or several parts, one of the first selection for your power system should be the cell count. This is important as it sets the basis for how much power you can extract from the system. Of course, a high cell count will lead to increased power. However, the cars are only so big, and weight may also be an issue.
The capacity of the battery will also ultimately determine the power capabilities. In general it would be best to select the highest capacity battery possible. This will provide a safer possible discharge rate keeping the LiPo cool and will be able to provide all the amps required.
The best way to determine and select cell count is by the Radio Control Car or Trucks size. This may also be refered to by scale size.
The chart available here provides a basis for selection. It is not uncommon for a specific model to run a cell count outside of this range.
Scale Cell Count Battery Size
1/16 2-3 cell LiPo 2100mAh-5000mAh
1/12 2-3 cell LiPo 2500mAh-5000mAh
1/10 2-3 cell LiPo 3000mAh-8000mAh
1/8 4-6 cell LiPo 4000mAh-8000mAh
1/5 8+ LiPo 5000mAh +
Once the cell count is selected, followed by the selected battery capacity, the last value to select would be the C rating. The C rating is explained more in depth on the LiPo Page. Select the highest discharge rate you can budget.