No, it isn’t really anything new. It’s the old Belkin Backup Battery Pack for iPod w/ Dock Connector. It has suction cups to attach to the back of the iPod, and the 4 AA penlights supply power to a weakened or battery-dead unit.

I have an old one lying around the house, and I’ve found it works for iPhones too.

I don’t know how long it’ll let the thing run without further testing, but I’ve determined that it does, apparently, work with iPhones as it does with iPods.

I let my iPhone run down, and then attached it. The usual warning appears that says the accessory isn’t meant to work with iPhones popped up, but I ignore it and tap no. Then the red battery indicator changes to plugged-in status (not necessarily charging) and pretty soon it’s fine again. (Like it does for iPods, it powers the iPhone but doesn’t charge it.)

There’s even a power level indicator so you know how the AAs are holding up. The thing attaches to the iPhone by two suction cups on the back, and it fits perfectly. The iPhone’s svelte no more, of course, and weighs three times as much, but it works. But all you’ll ever need are four AAs, and you’ll never be low batt ever again. Simple, easy to replace, relatively cheap and available everywhere. I will start bringing the device in my bag regularly, along with a coupla sets of penlights, and will be most excellent when I travel.

So you can provisionally add the Belkin Backup Battery Pack for iPod w/ Dock Connector to your short list of old iPod accessories compatible with the iPhone.

Will text it for longevity when I get a chance and report back to you. In the meantime if you see this in a sale bin somewhere, it’s going to be a good idea to pick it up.