The reason for discarding the good batteries may be very simple. I have no data to back me up, though, so this is just guessing: Let's say you have a gadget using four AA batteries. You take a fresh package of four AA batteries and insert the batteries into the gadget. When using the gadget, the batteries may not drain evenly. When the gadget stops working, the best battery or best two batteries may still have considerable amount of unused energy left. However, it is easier to replace the all four batteries rather than trying to figure out which batteries are still usable - and how much energy there is still available before you need to change the batteries again. Using the Batteriser will not help here either, because in practice you still need to replace all four batteries at the same time as you do not know the state of the individual battery. With a gadget using only one battery the situation is a bit simpler.