The older one -- I assume you mean the wider white one -- used *four* batteries. The new one uses two.
The main differences are size of keys, weight and number of keys. This new one is basically a MacBook keyboard with a cylindrical battery compartment. It's very portable, so you can use it with an iPad if you need to without too much clutter. If you need the keypad, there are add-ons that attach to the right side to give you the keys taken off.
I don't have any complaints about either one, but I would personally recommend the newer one. I think the keys depress easier and the batteries seem to last a lot longer.
