My brushless micro rally cars auto cutoff when the lipos get to 6v. Not sure if the crawler does though. Best to keep checking the voltage every few minutes on your first runs to see if it stops on its own.
In the micro t I used to run it until the car slowed down obviously. This used to be at about 6.2 volts.
This should fit your car. I used to use them in the micro t
http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html