The green advantage of rechargeable batteries isn't about the electricity and charging. It's all about using and disposing less of the materials that batteries are manufactured from.
A battery works by putting two different materials that have an electrochemical reaction together. Many of the common and most useful constituents for both disposable and rechargeable batteries happen to be heavy metals - cadmium, lead, or mercury, and in many cases the other chemical is caustic or toxic as well - sulfuric acid in your car battery. A car battery is big and has enough lead in it to make it economically possible to recover the materials (but you really wouldn't want to work in that plant). The amounts in an AA Ni-Cad battery (the Cad is cadmium) doesn't really work out economically as well. Even when recycling programs exist, most of these batteries will end up in a landfill with the bad stuff leaching into the ground.
So, using a rechargeable battery gets the exhausted battery out of the landfill, and causes you to buy less disposable batteries which means that you don't need to mine the bad stuff in the first place. Even if recharging it cost a lot, you'd still be way ahead. The fact that the cost to you over the life of a rechargeable battery is much less than the disposables it replaced is icing on a cake in a world where nobody wants to give you dessert anymore.
I just wish that they had rechargeables that matched the useage of instruments better. NiMHs work great in our Wii controllers, but in a guitar, not so much. Your mileage will vary - as somebody who doesn't play out anymore, I hate weekly maintenance tasks to keep gear going. Of course, if my battery conks out when I'm noodling, I guess that doesn't really matter much either!
David Fung
