At the supermarket, we look at the price/kg or price/l when comparing similar products. But we can’t really do that when it comes to getting an AA battery. For getting those, people usually go for names they are familiar with, such as Duracell or Panasonic, or go after attractive terms such as ‘PLUS’, ‘SUPER’ or ‘MAX’. But Denis Hennessy had other ideas. He bought a pack of every AA battery type he could find to do an experiment to see which brand provides the most bang for the buck.