The photo of the Solio charger shown on page 61 is different from the “new” Solio Bolt device sold by the company. Their web page doesn’t say how weatherproof the charger is, and the book doesn’t show photos of how the charger is connected to the devices we are putting in the bird feeder. That charger adds $70 to the cost of the bird feeder project, not including mounting and weatherproofing hardware. I have a 6v solar panel bought off Ebay that might be useful in this application, but it is probably too small to charge a 3.7v, 4400 mAh battery. I also have a larger solar panel and battery charger bought from Adafruit which with the battery included, cost a little more than $100. The challenge here is to connect these and mount them near the feeder without spooking the birds, harming them, encouraging dive bombing, visits from squirrels, and short-circuiting the devices after a few drops of rain fall or ice makes its powerful way into the tiniest of cracks and expands. (Water expands when it freezes.)
The choice of a charger to keep the Arduino and radio devices running happily is certainly an interesting one.