On Wednesday, April 22, 2020 at 1:45:05 PM UTC+1, Andy Burns wrote:
Jon Parker wrote:

Does that all make sense?
Even assuming you've got a 'free' 12V battery, what you spend on 3-way
switch, 2x sockets and a weatherproof enclosure will probably cost more
than occasionally running the car and plugging the air pump into the
cigar lighter ...

Not overly bothered about cost. Just something I've been meaning to get round to, and suddenly I seem to have a lot of free time...

Maybe not a car battery, perhaps a motorcycle or similar size.