Continuing the threads from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1257210571
Seems there are several elements at play here.
Driving an Uno from a solar cell / battery pack is the goal to avoid power lines to inconvenient places.
Factors (as I understand them)
a) Batteries like to either be giving charge or receiving charge, not both at the same time
b) Li-po batteries have very specific rules for charging
c) Solar cells give variable power, from zero, to some, to enough to drive a 5v Uno, to enough to *both* charge a battery *and* drive a 5v Uno
d) It is useful to have USB around to charge up when the battery is dead and it's dark outside.
An ultimate solution would
a) balance USB (when available), solar, and battery sources to give continuous 5V (or 3.3v) to the Uno
b) charge the battery from solar / USB as according to available source, while keeping the Uno well supplied.
c) report voltage of solar and battery for management and low-battery warnings.
d) do so unattended, as solar /USB power can change moment-by-moment.
e) not ignite the battery, at least, not often
Just imagine how a standard published schematic could free all those Arduino's from the tyranny of power cable tethering...
Could one of the brilliant honest-to-goodness engineering types comment or point to a solution? We'd all be grateful.