Dave Plowman (News) wrote:
Mate has a new Audi A2 - 1.4 petrol IIRC. Later this year he will be
going away in his camper van for three months - touring Europe. It
will be parked outside his front door in a private road.
Now I'd guess there's no way the battery will last that long. I could
go round there every couple of weeks and start it I suppose - but
what would happen if we just disconnected/removed the battery? I
could keep that here and make sure it was charged for his return.
Thoughts, please.

I would just leave it, it will be fine.
But if you want to mess about:
leave the battery on, you don't want to mess about with radios, immobilisers
etc. Get him to leave you the keys and once a month or so go and take it
for a drive of a few miles, 10 would be plenty.