That's one of the handiest little gizmos to come along in a while, especially considering how much battery juice running the navigation on my Galaxy takes. I can also use it to keep the charge up on my Sena helmet bluetooth.
There are a ton of those adapters on the market but Battery Tender makes about the best (IMO).
I bought one last year, used it a couple of times (it worked as it should) and then promptly lost it somewhere. Now I have a USB port mounted on the bars and wired to the bike but I would still like to find my BT one.