<p>I use the New Trent MP1000. 1100mAH rechargeable battery pack. It kept me 'found' on the PCT last year from Trail Pass to Sierra City+. It can supply 5V @ 1A using its standard USB plug. Out of the box it can be used with most Android (micro/mini) and Apple smartphones/devices. </p>
<p>With the new USB recharcheable Steri-Pen and an interface to a headlamp...etc...these battery packs (in general) might be even more useful! </p>
<p>A Steri-Pen adapter for a smartphone would be cooler though....phone, web, Email, LED light, book(s), GPS...and water sterilization.</p>