I just finished up some quick tests from a $40 four ounce Brunton Inspire LiPo USB charger with internal battery on the Nexus One. I am pretty impressed. My goal is to be able to recharge the N1 daily during one to three week hikes using solar power. Since the N1 probably expects a constant 500mA (for USB 2.0) or 1amp (using the wall charger) I started to look at other options for storing the sun's charge from my 6 watt or 14 watt panel. When I have the panel draped cross my backpack and am hiking in tree cover the power output will be sporatic. This might not be good for the N1 as it would at the very least be constantly powering on and off as it gets the interupted charging voltage. Enter the Brunton Inspire. It has a 3200mA 3.7V internal LiFePo (I think LiFePo instead of LiPo but not 100% sure) and the ability to charge it's internal battery from an external USB voltage level source or the ability to charge USB devices from it's battery (like the Nexus One for instance!). With a bit over 10 watt-hours of capacity, it should be able to charge the N1 from 0% to 100% at least one time, and possibly as much as 1.5 or 2 times. (the N1 battery has a rating of 3.7V at 1400mA). I did a test and even with the Inspire at 75% capacity it brought my N1 from 50% charge to 100% charge in about an hour and still had over 50% left according to the crude 4 led level indicator. I also did some testing to determine how the Inspire would respond to low wattage charging (simulating cloudy overcast days) and interupted charging (simulating walking under trees). In both cases it seemed to still dump whatever charge I could give it into it's internal battery. I simulated a cloudy day by only giving it 5V at 200mA from my bench supply and even this 1 watt of input brought it from the 50% level to the 75% level in about 3 hours. This could then be used to bring the N1 from 50% to 100% at night after the day's hike and gps/camera use.

I'll post more after I perform a few more experiments, but things are looking positive.