i did away with the AA batt pack soon after getting started in rc cars.
my first runaway came after a hard, 'high g force' turn caused my batt wire connector to come apart just enough to leave my throttle wide open from last radio command. the next few moments were not pretty and the carnage not on my 'want to do again soon' list. after 'WHAT THE..........'. i walked over to my car and tried the controls....the batt reconnected from the force of impact! i now without fail put a piece of electrical tape on the connector.
some servos will allow a spring or 'gummi band' to pull the carb closed but others won't decrease throttle if carb was 'open' when servo power ceased.