The independent variable we would manipulate would have to be the temperature. I would use the remaining battery life as the dependent variable (the thing we measure to see if it changed as we charge the storage temperature). We should store the batteries for a fixed period of time, say 1 month, and then have some batteries stored at room temperature as a control (to see what our baseline would be in the experiment so we know if storing them at colder temperatures, for example, makes a positive difference).
