I've seen these items before. It is a hand held unit that has a short set of leads going to the battery terminals. It has a self contained battery boost unit. It's for when you have a low battery and not quite enough juice to fire the motor and no other car around for a power source. It's NOT intended for long term cranking. I tried looking in the Summit,Jegs,Year One, etc. I looked at Kragens/Checker.

Where can buy one of these units?

I think most all autoparts stores have them.
I bought one at the Sears automotive center.

"auto battery booster" on yahoo will give you a good starting point.

They are becomming a popular item everywhere. Target, Wal Mart, Menards, Home Depot, all carry them now.

Like everything...you get what you pay for. Do your research. I read a consumer report like article that tested a number of these devices since they appear to becoming popular...and the tests showed that most of them were woefully inadequate and not even close to their performace claims. If I recall, they were of the consumer quality, not the professional, auto enthusiast, mechanic type quality.

Your local Napa store has them too.