An advantage of Droids is that you can carrying a spare battery for them. This is a fine option for someone who leaves the phone turned off, and only makes a few calls. For the usage I envision, I'd have to carry and recharge fistfuls of them!
Solar presents an opportunity to be completely independent of AC power. However, the Appalachian Trail is called the "Long Green Tunnel" because one is generally under a forest canopy. Most of the inexpensive panels sold to campers need to be at a right angle to the sun, and many shut down in the shade. Not suited to backpackers trying to make miles towards their goal during daylight hours. There are better panels that generate power in low light, some small enough to be fastened to the back of a pack, but I'm not sure they'll reliably generate the power I'd need to keep up with my projected consumption.
(Update 3/5/12 - A fellow 2012 thru-hiker has tested the Goal Zero Guide 10 on the AT, in overcast conditions, and found it to be a viable option for keeping his iPhone 4S charged. Lots of discussion on Whiteblaze about the viability of the new generation, mono-crystalline solar cells that are more efficient than the older technology cells. Two of the Goal Zero kits with panels and battery packs cost $130-160, weigh 14.4-19.2 ozs, and recharge the battery packs in either 2-4 or 6-8 hrs.)
External battery packs are recharged from a USB outlet, or a wall charger. When one wants to recharge their device, they simply plug a cable into their phone's USB port, and into the battery pack. A fellow hiker, who spends weeks at a time photographing Alaska's backcountry, recommended New Trent, and independent reviews backed him up.
But, what capacity do I need?
The Incredible 2 has a 1450 mAh battery. We're looking at an average of five days between town visits, with the potential for a few seven day runs. Assuming I leave town with a full charge, and that I'd need to recharge the phone every 1.5 days, I have a worst case requirement of 3.7 recharges. Multiply that by the 1450 mAh capacity of my phone battery, and I need 5365 mAhs storage capacity. And, that's assuming I'm not recharging Mary's cell phone, or an iPod, or a Kindle ...
New Trent had just released the ACD66 when I was ready to purchase. It sports 6600 mAh capacity, a slimmed down design that hints at the iPhone 4, increased capacity to weight, and it was being offered at a discount. The ACD66 measures 4.5 x 3.5 x .75 in, and though the specs say it weighs 8 ozs, it registered 6.9 ozs on my scale.
No wall charger?
It doesn't come with a wall charger. It can be charged from a computer's USB port, which doesn't help me on my journey. Their customer support said that one can use an Apple USB wall charger, and the included instructions specify it's input at 5V DC, 1A max - same as the Droid. A quick inventory of our current crop of wall chargers found five that were USB wall units, and all of them met that spec. The Apple and the Kindle were the lightest at .75 ozs each. The Apple had the full 5V, 1A output, whereas the Kindle charger was slightly less. I ordered another Apple charger so that I can charge the Droid and the ACD66 simultaneously.
So, what's the penalty?
Total weight to keep that Droid recharged with regular use? Seven ozs for the ACD66, 1.5 ozs for two Apple chargers, and 1.5 ozs for two USB cables for a total of 10 ozs.
I charged the device yesterday afternoon, and plugged my phone in before I went to bed. There was no smoke involved, my phone was charged in the morning, and the device indicated it was still more than 80% full.
A few days later, I took a second charge off the battery. My battery was at 3% when I plugged it in. 1.5 hrs later, it was at 50%. At 2.5 hrs, it was at 77%. At 3.25 hrs it was at 95%, and at 5 hrs it had gotten to 97%. And the ACD66 indicated it was between 60-80% capacity.
So far, so good.
I welcome your comments, and invite you to follow our journey by plugging your email addy into the box at the right.
Addendum: See my subsequent post in which I discuss what I took, and how I trimmed it down [here].