Possible Uninterruptible power supply for Pine64's SBC's

[CounterPillow]

Ideally, a small, smart UPS would have a USB 2.0 port for monitoring. Plus, some pass through USB 2.0 ports, (aka hub ports), that would be powered from the UPS at all times. (Meaning they don't take host power.) This would allow people to charge their smart phones and potentially a tablet during a power outage, if the UPS had extra juice.

I think just directly using the I²C of the fuel gauge chip is the better solution if we're designing specifically for SBCs. They all have an I²C interface, and you'd still be able to charge your USB devices through the powered on SBC. Saves on cost since we wouldn't need an additional microcontroller, wouldn't need to write yet another driver for its USB interface, and makes this an easy solution to just hook up to every SBC you own. The only downsides I can see is that I²C doesn't do enumeration so you'd have to apply a device tree overlay (which is simple enough to do with mainline these days), and that you'd be charge limited to the 500mA or whatever the USB ports on the SBC output.

As for current it can provide, if we go for 12V with lead acid and no regulation (relying on the onboard PMIC of the SBCs to handle whatever voltage drop the battery can have) we can basically draw whatever the battery can take, which is a lot. (>100A typically it seems?) Though that might be a bad idea because of how quickly voltage will drop, and limits us to 12V batteries and 12V SBCs.