What chemical leaks from batteries?

05 September 2013

Question

I have a question about alkaline batteries. I recently unwrapped a set of battery powered lights, and I saw that we had left the batteries in all year. The batteries are a well known brand and they looked like they had leaked. There was a white powder around the contacts of the batteries and also on the contacts of the lights. What is this powder? Is it harmful to touch? What would be be best way to clean this powder away? Do we need a chemical help such as lemon juice or something? Will the powder be harmful to a new set of batteries that I insert? Keep up the great work!
Rob from Leeds.

Answer

Laura - Okay, so what's actually happening here is the electrolyte from the battery is leaking out. So, you think of batteries, it's sort of school level chemistry that you've got a reaction going on between two metals and there's some sort of electrolyte in the middle that's allowing charge to be transferred between this two sides of the battery. That usually in your normal alkali batteries is potassium hydroxide usually or something like that. Eventually though, your batteries do keep reacting even if you've not connected them up. They react very slowly, but they do leech a little bit and there could be side reactions, and eventually, these things can just sort of pop open, at which point, your electrolyte comes out.

Chris - Is it nasty?

Laura - Potassium hydroxide is not very nice. It's an alkaline. It's quite caustic. However, it then reacts with carbon dioxide in the atmosphere. So actually, what you're seeing is those white crystals. That's actually potassium carbonate and that's actually potash. That's the main component in potash.

Chris - That's good for garden.

Laura - I wouldn't suggest necessarily knocking it off and putting it in your vegetable patch or anything. But probably, don't start licking at batteries or anything like that, but just dispose of them. If there's any on your contacts or things, you can start trying to wipe that off potentially with lemon juice or something.

Dominic - And I guess even if it's potash on the surface, underneath, you've still got the potassium hydroxide you don't really want to knock that surface off.

Laura - No, quite. So, that's why you want to use say, something like a weak acid to try and neutralise it as you're washing it off. The other thing of course is that these things can start creeping in to electronics and so, you can actually - if you've left your batteries in something for long enough, you can start really messing around with your circuits and degrading them.

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