To check the effect of cold temperatures on the battery's ability to start a car researchers purchased a battery from Sears and one from NAPA auto parts. They disabled a car so it would not start, put the car in a warm garage, and installed the Sears battery. They tried to start the car repeatedly, keeping track of the total time that elapsed before the battery could no longer turn the engine over. Then they moved the car outdoors where the temperature was below zero. After the car had chilled there for several hours the researchers installed the NAPA battery and repeated the test. Is this a good experimental design?

This is a good experiment, however there are a few flaws

Explanation:

In this experiment, the battery is not replaced. Which can then affect the experiment if it had sustained damage from the failed attempts in the garage, and then being moved to the second scenario. Another possibility is that the battery was faulty from the start, which would definitely affect the results negatively.

Another flaw would be the temperature. The first scenario of a warm garage is fine, however after being moved to an environment below zero, the water in the car would have frozen, and many other systems would be impaired. Therefore the starting of the car would be influenced by more than just the battery.