On Thu, 13 Aug 2015 12:52:50 -0700, John Robertson wrote:

Potassium Hydroxide - an alkaline (Alkaline batteries after all). Wash
off with a mild solution (50/50) of white vinegar and water, scrub, and
rinse with clean water carefully.

http://flippers.com/battery.html

That article was nice, but I'm always suspicious when someone suggests
idiotic things such as "pure water" (goes with "kosher salt" in my book,
or with "organic eggs", etc.).