Don't try this at home.

After being at the shop, I always have a shower and wash my clothes. This time - my car key went in with the clothes. "Oops" didn't quite cover it. The spare didn't work either.  The upside is that I went over to the Toyota garage near Peacehaven (hence yesterday's blip); they showed me how to open keys and put new batteries in. I had to put the internal bits of the wet one in rice overnight, reassembled, and to my great relief both keys now work!   Cost £12.