Re: If a battery fails when there is no-one to see it ...
hi,
The LEDs are good for applications whenever you can see the thing (e.g. under the lid of a Pibow case), and as someone else mentionned they take very little power.
We do have an ADC measuring charge already :-) and we pass that data to the Pi via a 3-bit value on GPIO. This is enough for basic operation, but as we add more features it gets a little tight, and we also want to allow configuration on the Pi itself -- so we need to pass data back to the board. Your suggestion of I2C looks like the best option for this -- thanks for the confirmation.
Re. other LiPos and so on, yes, there are lots -- none that I know of tell the Pi when the battery is low and needs to shut down, but no doubt they'll come :-)
Thanks for your interest!
h