Step 3: Choose a Lithium Charge Controller  As reactive as
Lithium batteries are all you really need to be safe is to have
a circuit that controls the voltage going to your battery.
While you could make your own charge controlling circuit, it's
far easier to just buy one that you know works. For this you
have several options.  Adafruit is now on it's second generation
of Lithium Charge Controllers that have several options for
power input. They're very nice, but a bit on the large size. Not
at all small enough for our Altoids tin sized enclosure.  I sell
some small Lithium Charge Controller Modules on my site. These
are the ones I use in my kit and in this guide. I like them
because they're small, simple, and have status LEDs for charging
and when the battery is full. Like the Adafruit charger you can
also use the USB port on it to charge up the Lithium Battery if
you lack sun. (Something that is very handy for any solar
charger.)  No matter what you use, be sure that you know how to
use it and what goes whe