I've been researching solar chargers vs. external battery packs and thought I'd share the info I obtained.
First of all I decided against buying a solar charger. From what I've read of other people's experiences solar is not the right choice for a thru-hike on the AT. The nickname "the green tunnel" might suggest the larger of the issues. However, given the size and weight of solar chargers, the messing around trying to get them the proper sun, and the low output (related to not obtaining a full charge), it seems to me the external battery pack is the way to go. It sounds as if in order to get a decent solar charge you really need a large panel - larger than is feasible for a thru-hike. From the quick searches I've done they appear to get extremely expensive when you go big. I know there are those who will disagree with my rationale for choosing an external battery pack over a solar charger, but the main point of this post is to share the info I found pertaining to the battery packs.
I looked at a few different makes (including the Brunton Inspire) and the best external battery packs I've found are by NewTrent. They are currently in the process of updating their website and swapping out older models with newer ones, so their website isn't entirely accurate (at the time of this posting). The following info I obtained from contacting their customer service department via phone and email.
IMP500 - 3.9'' x 2.8'' x .69'' 5000 mAh 5.1 oz - $35 output 5v@600mAh
IMP50D - 4.3'' x 2.79'' x .64'' 5000 mAh 5.2 oz - $43 output1 5v@500mAh; output2 5v@1a
IMP52D - 4" x 1 3/8" x 7/8" 5200 mAh 4.4 oz - $40 output 5v@1a (only one port)
IMP60D - 4 5/8" x 3 1/8" x 5/8" 6000 mAh 6.2 oz - $40 output1 5v@1a; output2 5v@2a
IMP70D - 4.4'' x 3.45'' x .6'' 7000 mAh 7.0 oz - $46 output1 5v@1a; output2 [email protected]
If your current phone wall charger is one where the cable separates from the plug (a USB connection) you can likely use that to charge these units from a wall outlet. The AC charger/plug for these needs to have 5V, 1A output. You simply use the plug from your current charger and connect the supplied USB cable to it.
*D in the model name = dual port (except IMP52D)
*The prices are the best I found doing a quick Google shopping search.
For my purposes my phone's battery is 1300mAh, so I'd probably get at least three full charges out of one of these batteries (likely more with one of the larger units) using the low output port. The plan is to simply find a wall outlet to charge the external battery pack while in town. I've read accounts of people using these on the trail and getting at least 2-3 full phone charges out of them.
Some of them have dual ports; one for low output, one for high output (i.e. high output to charge an iPad). They come with a USB charging cable and a mini & micro USB adapter (photo attached).
I spoke/emailed with Robert in their customer service department. He was extremely helpful. I explained I had heard the specs weren't accurate on their website. He went to the warehouse, got each of the units, weighed them himself and sent that info to me. A coworker of his had recently re-measured the units so he sent me those dimensions. I also verified with him the capacity and model names of each unit and asked for the high and low output levels, which weren't listed on the website.
By the time you read this they may have updated their website, but I thought I'd share my findings for those who may be interested in purchasing an external battery pack, since it took quite some digging to get all this info.
Below are photos Robert took with his phone of the items he gathered from the warehouse. One shows all the units lined up; the other shows the included cable and adapters. The order of the units (from left to right) are: IMP70D->IMP60D->IMP52D->IMP50D->IMP500
NewTrent battery packs.jpgNewTrent cables.jpg