Another thread on safety, some useful info.

[Robin3]

Originally Posted by StuM

For 20 bucks or so, well worth stuffing in the grab bag:

wind up phone charger | eBay

THanks, would work I guess but I thought I had seen a small plug in battery booster thing presumably containing another battery to piggy back on the internal phone one.

something likelike this one? Amazon.com: RAVPower Element 10400mAh External Battery Pack Portable Charger Power Bank (Dual USB Outputs, Ultra Compact Design), for iPhone 5S, 5C, 5, 4S, 4, iPad Air, 4, 3, 2, Mini 2 (Apple adapters not included); Samsung Galaxy S4, S3, S2, Note 3,

[Richard_W]

The advantage of a hand crank charger over battery pack is that it can supply power as long as you are able to crank it. The battery pack will eventually discharge, even in storage. The solar/wind charger requires weather conditions. The crank works as long as you are able to work with it.