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Andy says, I recently read your GPS buying guide and I'm interested in what you suggest for keeping the batteries charged on several day trips. My GPS has an 18 hour battery life which allows me to leave it on for parts of each day, but it won't last for my typical 3-4 day trip. I could carry extra batteries, but that becomes a hassle.
If only someone would invent a more universal power source for all these battery powered devices we can't seem to live without. Carrying spare batteries is by far the cheapest solution, but becomes tricky if you bring spares for a variety of devices and almost never offers a solution for cell phone users. I know even when I'm going to trade shows I find myself annoyed by the number of extra batteries and charger cables I need to bring to keep everything working, so I can only imagine carry extras like this on a backpacking journey becomes an even bigger headache.
One solution I carry as a backup for power is a solar charger, which may seem a little odd considering Seattle's reputation for rain, but you never know. I'm partial to the iSun products, which don't provide enough juice to power a laptop, but are capable of reviving many cellular phones, are specifically rated for Garmin GPS units and also handle power enhancement for things like two-way radios, MP3 players and Nintendo portable gaming systems. As long as your GPS has a rechargeable battery and isn't one with replaceable AA batteries, you'll be able to revamp your battery life for a few hours with something like the iSun charger connected and placed in full sunlight.
The primary reason I like the iSun products is because you can daisy-chain several together for increased power. Another reason iSun's product line is more interesting is it powers devices directly rather than pushing power off to a cumbersome battery pack (making it lighter in your pack). A variety of adapters make the iSun unit compatible with virtually any device, with an accompanying adapter for connecting car chargers as well. Depending on where you plan to use your GPS, it may be possible to connect a solar power supply and run the GPS directly off of the power from the solar cell. The units are rated to function from -40 to 176 degrees Celsius, which should mean you can still charge your GPS from the top of most of the world's mountains.
