What causes batteries to corrode inside a flashlight?

I recently found a flashlight that was ruined due to the batteries leaking and eating away the insides of a flashlight. I was wanting to know why this happens? Also, is it a crap shoot (in other words, one never knows if/when it will happen, it just does, without warning)? What can I do to keep this from happening, other than putting batteries in a flashlight when I intend to actually use it, otherwise, keep the batteries out?

Thanks for the information.

I have been wondering about this for a while, too. My professional opinion is batteries leak after they are discharged all the way. In other words, if you put a good battery away, it will not leak, it'll just die and the goo inside dries up. If the battery is discharged, some of the metal casing (anode? cathode?) has been used up, making a weak spot that eventually eats through and leaks. I have a battery from 1924 that's in pretty good shape. It's deader than dead and has not leaked. I assume it was put away "alive" way back when.
Kirk

I believe it is caused by gas build up in the cell. A lot of batteries seem to produce some hydrogen when being used and even more when being abused. Usually they seem to leak from the end seals. I even have seen some alks swell up and push out the plastic plug on the negative.

Ok, answer this one -- (sort of off-topic):

Three time my ArcFinity actually "popped" open inside my pocket. I could feel it every time and once it was so loud that a coworker was able to hear it. The head would actually get expelled from the battery tube. Nothing was ruined -- it just must have been slowly unscrewing inside my pocket.

After the third time (some people just don't learn so fast) I got in the habit of opening it once a day just to bleed whatever the heck was in there. When doing this there would still be a very audible "pop".

This particular ArcFinity was built with one of the original Infinity tubes which are longer than the present ones. Because of this I had a washer built-up with solder and electrical tape instead of just a simple washer.
I also had a Post-It note wrapped around the battery to minimize rattle.

What do you suppose was causing the excessive gas build up?
The glue from the electrical tape, the glue from the Post-It, or the battery itself?

I think it helps to keep the inside of your flashlight free of moisture. Some lights have hydrogen vents to let out moisture and hydrogen gas build up.

I also find that Ray-O-Vacs tend to leak less in a flashlight. They will also replace/refund your money to buy you a new one.

The way it was explained to me was that the batteries leak what gas? Answer: hydrogen. What else is inside the battery housing? Answer: oxygen. What is Dihydrogen Monoxide (DHMO) made of? Answer: 2 parts hydrogen + 1 part oxygen...There you go...the batteries are making their own DHMO, which is CORROSIVE!

There's a Material Safety Data Sheet for DHMO on the website posted at the bottom of this message. (You know it's a constituent of many known toxic substances, diseases and disease-causing agents, environmental hazards and can even be lethal to humans in quantities as small as a thimbleful and causes corrosion in flashlights). Seriously, EVERYONE should check out this site:

http://www.dhmo.org/facts.html & learn the facts about safely dealing with the Dihydrogen Monoxide (DHMO/Hydric Acid) in your torches!

Various CPF'ers have posted that alkaline batteries that are run down below 0.8 V per cell with no load are prone to leaking.

If you throw away alkaline cells before they drop below that level, you are far less likely to suffer from leakage.

That's the most important rule on leakage I've learned so far (other than don't leave alkaline cells unattended in devices for extended periods of non-use.)

So, the best thing to do is to check the batteries in your flashlight(s) occasionally to make sure all is well. I don't have a HUGE number of flashlights (around 30 +) but this could take a while to do. The last thing I'd want to find is corroded batteries in one of my precious little lights.

I have often wondered if a single cell light like the Ultra would have the same problems.

The battery is not actually "engaged" when it is off, and since there is only a single cell, there is no possibility of the battery interacting with another cell.

Does this only apply to alkaline batteries, or will it happen to Lithiums as well?

ikendu/Stefan...good questions..I wonder if there is any information on the battery manufacturer's sites? If I get some time, perhaps I'll prowl around, unless someone "beats me to it"??

Further information about Dihydrogen Monoxide (DHMO is corrosive you know and is a constituent of many known toxic substances, diseases and disease-causing agents, environmental hazards and can even be lethal to humans in quantities as small as a thimbleful. ) here:

http://www.dhmo.org/facts.html

Edit: I see now!

However, might I point out an error in the DHMO website -

It's the hydronium ion, not the hydroxide that is present in things like sulfuric acid, nitroglycerine and ethyl alcohol that gives them nasty properties.

Onyx...do I need to talk to you "privately"?

Dihydrogen Monoxide (DHMO) is a colorless and odorless chemical compound, also referred to by some as Dihydrogen Oxide, Hydrogen Hydroxide, Hydronium Hydroxide, or simply Hydric acid. Its basis is the unstable radical Hydroxide, the components of which are found in a number of caustic, explosive and poisonous compounds such as Sulfuric Acid, Nitroglycerine and Ethyl Alcohol.

http://www.dhmo.org/facts.html

I wonder if heat contributes to leakage. I've had two batteries leak in the last six months. An AA cell in an electric shaver, and an AAA cell in a flashlight both leaked while stored in my car during the summer. The alkaline cells were fairly new, less than a year old when they leaked.

rodmeister, Heat can most certainly cause almost any container and contents to expand and/or leak depending on expansion rate vs. container size... An installed vent could help relieve pressure, but contents will still expand and possibly leak depending on the size of any containment space built into the container itself.

shame on you sigman But you are right this evil DHMO (also called H2O) compound is endangering the planet. Coastal cities are particularly at risk.

Back to "reality", does the orientation of the batteries contribute to corrosion in some way? Which was is 'up' anyways?

Getting back to the heat, which is no longer a problem in winter: I'm replacing all my alkaline batteries with lithiums in my car. I'm also considering some kind of small insulated box for my car lights.