16: Battery Backup

Post 11 corrected
** revised again 7/16/15 **

When I tested my battery backup circuit (post 11) I failed to let the systems run on both USB input and battery for long enough. Turns out with 5V/1A input from my USB hub the setup drains the battery. And when that happens the USB output drops to 4.10V. Not nice. However, USB input of 2.1 Amps seems to correct the problem.  Wrong again: Anyway, the setup pictured only works if the USB out draws less than 500mV. None of my Nano test setups take this little -- nor does my Particle Core. So regardless of 5V USB input the the system fails when the battery runs down (USB output drops to 4.1V).

Gory details at http://forums.adafruit.com/viewtopic.php?f=15&t=76014

Most USB hubs don't provide 2.1A outputs. So I ordered a 5-pack of 2.1A wall plugs. I'll let you know how they work long-term.