If you put lemon juice (or any other citrus fruit juice) it will slow the browning process known as oxidisation.
oxidisation
Oxidisation of the iron compound
Oxidisation.
Oxidisation
Rancidity ,corrosion
oxidisation
Patina.
It is a metallic surface that will not discolour or stain, especially be oxidisation
Oxidisation, which is when the moisture in Oxygen comes into contact with the metal.
Oxidisation, which is when the moisture in Oxygen comes into contact with the metal.
There are many types of flashlights now, so new circuitry can sometimes be a problem. However the commonest problem in all kinds of flashlights is oxidisation on the cathode (negative) spring.