Add support for emergency power-source

[SvenRoederer]

to get a beer even when there is no mains

[MicDiFebo]

The first and very simply USV only consists of a battery looped in the powerline. That would keep the BC running for hours, but it is not possible to open the valve with that construction.

[SvenRoederer]

Not sure if a small solid car-battery is an option for the valve (or two 6V motorcycle batteries)

[MicDiFebo]

Surely that will work, but that is much too big for our enclosure. :-)
In General we can think of using a 3cell lipo-battery like it is used in RC-modells (I used this in my Heli- and Quadcopter), but then we need a separat charging-electronic, which is a bit more complex for 3cells, because they must be balanced during charging.

[SvenRoederer]

at the end, we can just replace the wallwart (isn't it 12V DC) by a external battery, just by repluging. As the Pi will keep running by the mentioned USB-type UPS a short moment w/o external power is fully acceptable.
Something like this 12V 5Ah-type might be enough and we can charge by a regular bench supply.

[SvenRoederer]

We should also keep in mind, that w/o mains, the cooler will not run and only a limited amount of fluid can be drafted "corrrectly". So there is only a limited duration we should be able to draft w/o mains, e.g. 1h / 5l beer.