Next day he was still on the wall but in a different place. This also is not a problem. I thought he'd chosen that wall as His Place and was settling in. I told the lady as much, and left her to it confident the bat would be fine.
It wasn't until the third day that she told me the wall was actually an internal wall of a shed that was locked up every night. No wonder Jack was hanging around - he couldn't get out!
By the time I rescued him he'd lost a lot of weight, tipping the scales at 10g instead of the more normal 15g. So he's in for a week of R&R. Last night I fed him 8 meal worms but he was much nore interested in drinking water from the syringe. Tonight I expect he'll eat more. I want to see a fat bat by this time next week, then he'll be ready to face the winter.