Question

You are interested in determining which of two brands of batteries, brand A and brand B, lasts longer under differing conditions of use. One hundred Fenix flashlights are fitted with brand A batteries and 100 Olight flashlights are fitted with brand B batteries. Each battery is used for 72 hours straight. The battery life is then measured for each battery, and the average battery life for the two brands is compared. What is wrong with this experimental design?

Answer 1

The flashlights should be the same for both branches. If one battery last longer than the other maybe that is because of how each flashlight use the energy of them. You can try, for example, mxing the flashlights so that 50 of each kind  are fitted with each of the brands.

Another problem is that you cant meassure correctly the lifetime of a battery if it lasts longer than the 72 hours you are using it.

Also, you might want to study more than the mean lifetime. You can try finding the standard deviation of each sample for example so that you can see if there is a branch that suffer more about bad conditions of use and is less consistent providing a good preformance.