Skip that charger cabel and check out this one:
http://www.walmart.com/catalog/product.do?product_id=5607971
You get two extra batteries, the charger base, and a charge and play cable. I got mine in the store for $29.95.
And my son is a big gamer, and the hard drive rarely gets used. Save the cash and get an extra game or two. I had found a link last year, when I was buying his, that you could adapt a computer hd into the 360. And they are dirt cheap compared to 360 HD. I will check my favorites later and see if I still have it. (if you are interested)