I have tested the setup shown in post 79 (explained better in my Arduino blog post 11: dicks-arduino-nano-travails.blogspot.com).
First, I tried it with an Arduino Nano (most expendable). Worked.
Then, my Spark Core setup. Worked, too. I let the battery run down on this test. I'm not sure how long that took (+2 hours?) and I had not recharged the battery after trying it with the Nano. Then something nasty happened: the Powerboost 1000 sort of hiccuped off and on powering the Spark back on for a second each time. Good old Spark survived this but I wouldn't bet on a Pi doing as well. Also, the Powerboost was fried (Adafruit replaced it).
Finally, on a Raspberry Pi B (rev 2) with a fair number of GPIO pins connected including a WIFI dongle, a Pi-powered relay switch and a 7-segment clock display. I let it go nearly an hour then the Pi stopped running while the Powerboost still showed its green "powered" LED. Hummmm.
This is what I want for my Pi setups:
1. Detect fail (eg: by reading photosensor pointed at extern power light on Lipo charger).
2. Send out email and text msg warnings to humans (if internet-connected):
"Power fail. Shutting DOWN! date/time".
3. In Linux: kill my running processes (especially anything writing files):
% pgrep -u pi | sudo xargs kill -9 (for user "pi").
4. Linux: % sync; sync; sleep 5
5. Shut off 5v power from battery before voltage drops but so the system will restart when external power is restored.
Suggestions? Will the "Pi Juice" (see Kickstarter) do all of this?