Originally Posted by HogWild
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.
I agree. Not necessary. I forget what a pair of AA batteries is rated for in SPoT -- I think I recall seeing 2,000 transmissions in there somewhere. Well, let's say the real number is half that. That's roughly 10,000 minutes of operating time in tracking mode, or about 14 12-hr days in the saddle. Going to an external DC source seems...not necessary. Take an extra pair of batteries if you're really, really worried.