Originally Posted by jeffmccracken
I'd like to rig the unit up to run off bike power stepping down the bike voltage to 3V.
It's hard to imagine why you would need this. The SPOT isn't like a typical GPS unit that can run a set of batteries down in a matter of a day or two. The SPOT batteries will last for weeks of continuous use. Plus, with the wired connection, you loose the option to walk away from your bike with the SPOT in hand. And, when you're in the middle of nowhere, and your electrical system (and thereby the SPOT) dies on you, leaving you stranded, that may be the exact time when you need the SPOT to work. Add to that the fair chance that you'll fry the SPOT while testing the regulator circuit, and it seems you're at high risk of the SPOT not being able to do what it was intended to do.
If you still think it's a good idea, all sorts of voltage regulators are available at www.digikey.com