We have a 'kitchen cleanser' here in USA with Barkeeper's Helper name, that contains powdered oxalic acid and is used for cleaning stainless steel counters and sinks. When mixed into a paste, I have used it on a number of occasions on cotton-tipped swab to clean electrical contacts after battery corrosion (such as flashlight or small battery-powered electronics) appeared when my wife put something away for a year without battery removal...dab it on, let it sit on the contacts for a minute or two, swab with clean, water-moistened swab, blot dry, the contacts are nice and shiny and operation of the device is restored.