Smaller RC cars always use AA cells as their power source. The problem is that if you leave the cells in there for too long, you will eventually find a mass of green corrosion on the contact plates, preventing electricity to flow through the system. This Battery Contact Corrosion problem is unavoidable unless you change the power susyem to using something else. In this example we solder a JST connector to the contact plates so that a small 2S lipo can fit in to power the car. You need to be careful with the polarity. The red wire goes to the front plate and the black wire goes to the spring at the end of the system.
In theory, four pieces of AA cells can produce 6V power total. A 2S lipo offers 7.4V. This is a small over voltage configuration which would not affect the electronics of the car.