I know someone who actually has a few of these devices - they are big into their FWD'ing - they have solar panels on their roof and spend days 'off the grid'.

I know someone who actually has a few of these devices - they are big into their FWD'ing - they have solar panels on their roof and spend days 'off the grid'. Another (more common) use case is people that take their caravan out on the road. Many have a plug into the car that keeps the caravan fridge powered on when driving. For me, I wanted to keep track of the voltage of the battery in a caravan when not connected to mains power.