Goal Zero Sherpa 50

When paired with the Boulder 15 solar panel the Sherpa 50 is more than enough to keep 3 cell phones and other gadgets topped up on a 3 day motorcycle ride through Colorado and Wyoming (even if it is covered in mud half the time).  I have used the Sherpa 50 for a couple of years through all sorts of conditions and it is the most reliable of my many battery packs.