Spotted a rather wet and slightly corroded 18650 in The Narrows down Charterhouse today.

I nearly brought it out, but I recall people saying that they can explode when wet, so I left it under a rock instead.

Any thoughts? Is it safe to bring out or might it explode if it gets knocked?
Is it a hazard where it is?

And before anyone asks, I didn't think to look at the brand, but it was green if that helps  :-[

I doubt that its dangerous, but very likely useless if corroded.
What you would probably get is an electrolytic effect between anode and cathode, very close at the top. This would hasten corrosion and drain the battery.
Over discharge can render them dangerous, but the fun would start on an attempt to recharge.

Its an interesting question actually, and one I don't have real answers too. If anyone knows more I would be interested to hear it.

Thanks Roy.

Assuming nobody has any different advice, I'll bring it out next time I'm down there and make sure not to try charging it 

Bring it out, i'm sure it will be fine.

I carried around an 18650 with a slight scratch in the side in my laptop bag, I think the positive and negative shorted on my laptop. So now I have an ever so slightly melted laptop.

But I did carry the bugger around with me for a couple of weeks!

I found two of these 18650 batterys in Pant Mawr Pot today, and Yes I did bring them out ready to be recycled at the Recycling bank.

Just a heads up warning about these batteries in use.

The cheaper OEM cells have only a thin outer wrapping, retailers will fit a protection board to the base and then their own outer label. The outer label will act as an extra layer of insulation.
Risk is torches that load the cells in series, nose to tail. If the body of a cell shorts to the aluminium torch case what you will have is a pipe bomb. If you think about it the negative body of the upper cell is the positive of the lower.

Short circuits are normally often not catastrophic as a single wire or copper strip on a pcb will melt, in effect acting as a fuse. A cell body to aluminium torch case is a different beast.

Over discharging a Li Ion cell can cause internal short circuits, but obviously by then capacity is low and hence so is the amount of energy available for release as heat. Attempting to recharge is potentially dangerous. Cells with voltages of less than 2.5V should be scrapped, they be NG anyway.

All batteries are dangerous if short circuited, this can cause fire and injury. However Lithium Ion can suffer from an effect known as "thermal runaway".

18650 cells are Lithium Ion Phosphate which is generally the safest form of Lithium Ion battery. Lithium Ion Polymer is an entirely different chemistry and some batteries of this type have been known to explode if subjected to violent shock.

Hello Roy, please could I ask where would you say is a good place to read about the Lithium Ion chemistry?

Ian Ball said:

Hello Roy, please could I ask where would you say is a good place to read about the Lithium Ion chemistry?

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Good old Wiki is a start

https://en.wikipedia.org/wiki/Lithium-ion_battery

https://en.wikipedia.org/wiki/Lithium_polymer_battery

Torchy the battery boy
http://www.torchythebatteryboy.com/

and manufacturers data sheets, typically Samsung, Panasonic and Sanyo

Plus of course, anything else turned up by web browsing, as long as its factual not some of contrived rubbish on YouTube

There's also battery university, which will tell you, in detail if you want, about pretty much any battery/ell technology I can think of. Even the really weird ones.

https://batteryuniversity.com/

Well, the wet 18650 was removed today and didn't explode on the way 

royfellows said:

18650 cells are Lithium Ion Phosphate which is generally the safest form of Lithium Ion battery. Lithium Ion Polymer is an entirely different chemistry and some batteries of this type have been known to explode if subjected to violent shock.

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Very few 18650s are Lithium-ion phosphate (LiFePO4), the majority are Lithium-ion Cobalt (LiCoO2).

Phosphate is the safest form by far, but it has a lower operating voltage than the standard LiCo cells. You can not mix and match cells or chargers. The good news is that whilst phosphate cells are available to Joe Public, he'd have to go looking. Phosphate cells have a lower energy density, handle less current and are more expensive than their Cobalt based cousins.

Li-Polys are usually distinguished by their soft cases. They are the more dangerous of the group. They have the highest energy density and therefore the most potential to go pop. This is what you'll find in your phone, safely sealed away from prying fingers.

All Li-ions require a safety circuit to disconnect the cells if the voltage gets too high or too low, or the maximum charge or discharge currents are exceeded. This is the secondary protection circuit. The primary being that the charger / load itself shouldn't be abusing the cell.

All (reputable) 18650 have tertiary protection inside the cell. A over current / over pressure device will permanently disconnect the cell and vent gas if the cell internal pressure is too high, or if the cell is short circuited. I wouldn't like to vouch for the reliability of this on clone cells.
I've seen nails driven through cobalt 18650s to test their safety (do not try at home). I've seen them crushed and heated. They're quite resilient.

Short term immersion shouldn't be a safety issue to a 18650. It may cause the cell to over discharge, it's certainly not going to do it any good. I'd be worried that long term immersion could compromise the internal safety device.

Yes I'd happily remove a discarded one from a cave, but I'd keep it where it could be thrown away if it started getting hot.


Roy's absolutely correct in his advice about the plastic sleeve. It's not wise to rely on that alone as insulation.

An interesting and informed post. I was a bit behind in my chemistry.

To be precise, the chemistry type is in the letters of the battery designation.
I am using:

Sanyo Panasonic NCR 18650 GA. So, that's 18 X 65 mm, NCR (Nickel Cobalt Rechargeable) which is a new standard recently introduced. These will often be encountered as re-wraps, or rebranded for retail sale. The Sanyo Panasoinic as an OEM (original equipment manufacturer) 10A max discharge, but high capacity.

Samsung INR 18650 30-Q, same size as above, and OEM. INR (Lithium manganese nickel rechargeable) These are a high discharge battery suitable for my big bat cookers. 15A max discharge

Sanyo NCR 207000B. 20 X 70mm same chemistry as the first, 4000 mAh and 15 amp max discharge.

Some needs to know

Beware of some of info out there on the web. For a query re a specific cell refer to manufacturers data sheet. Internet search should turn one up.

The different individual cell types have different safe maximum charge and discharge rates.  If in doubt charge at 0.5C where "C" is the capacity. Although some will charge at a hell of a lot higher its best to play safe if in doubt.

Fakes, duds, and recycled laptop cells. Genuine is easy to spot as they will ship at what I call "factory voltage' or could also be accurately described as "storage voltage". So a batch should all read the same voltage on a meter which will be 3.46V or 3.47V. I would not expect a drop of more than 0.01V after some storage and all cells in a batch to be equal. This condition is impossible to reproduce and even in the event that they could be carefully charged to this exact level there would be a drop in transit on fakes, junk, and duds.

Welcome MikeVeal, 2 posts and 2 very interesting ones 

Thanks Gents.

Roy,
The consistent voltage you're seeing is very likely a result of the IATA UN38.3 regs:
"On pain of a slow and tedius death, thou shalt not ship by air any lithium battery charged to more than 30% of its capacity. Unless of course that battery is installed in a product, in which case; fill yer boots."
It makes no sense, but them's the rules.

It's actually quite easy to charge batteries to that point. Coincidentally, today's job for me is to debug my code for a manufacturing rig that does just that.
You're right in that the batteries in a batch should all be fairly close together in voltage but cobalt based batteries can lose up to 1% capacity per calendar month of storage though, it's very dependent on temperature. 

I don't think there is any attempt by the sell manufacturer to match the cell voltages in a pack. Time in a charge / discharge rig is very expensive. However, they do have to comply with 38.3 what you're seeing is likely the result of them doing the absolute minimum to comply with that.


I should probably let you guys know what I do and what my exposure to batteries is. I'm an electronics engineer, I work in computer storage. The industrial stuff that you find in server rooms. I used to work for IBM, but have gone to a smaller player (who pays more).
I've been designing systems using lithium packs for about ten years. I design both the systems and the packs. We use them to keep our main processor alive when the mains power fails, so that we can gracefully save away any customer data that we're holding in volatile memory.

I used to  be an active caver, but haven't been for quite a few years. One of my buddies is pestering me to take him down Stoke Lane, I quite fancy it and I'd like to get back under.

You are very welcome Mike I wonder if you will find yourself flooded with battery related questions!