some have
batteries inline, others have a small battery where the battery actually would be. USB provides 5v and 12v, common voltage for atty's is 3.7v. The USB current keeps the 3.7v source delivering.
I got mine from ElectronicAsh for $12.99 Works great, delivered to my door in 3 days from order date by usps priority. This one does not have a battery inline which may turn out to be negative because you can probably replace the inline one, but I only use it when the computer is on so it should last a long time. yes it does work for a few puffs with the computer off and it flashes like a regular battery when it is discharged.