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Salt water LiPo disposal - bad idea, or really bad idea?

#1
Friends, Romans, FliteTesters, lend me your ears, I come to bury salt water LiPo disposal, not to praise it.

Yes, my friends, salt water LiPo disposal is a bad, bad idea. Sure, on the surface it seems like a good concept - after all, salt water conducts electricity, so it makes sense that dropping the battery in salt water will discharge it. But the devil is in the details and the detail, in this case, is electrolysis. You see, salt water and electricity have an amazing talent in the field of dissolving metals, including the tabs on the LiPo cells that actually conduct the electricity. And once those tabs are dissolved, no more discharge. That's the real problem - the tabs on the cell tend to dissolve before the cells are completely discharged, leaving you with the worst of both worlds - a cell that's still got a charge, and no way to discharge it.

"But", you ask, "why does everyone recommend using a salt water bath to dispose of LiPos? Where did this recommendation originate?"

To answer that question, we need to take the WABAC machine back to the dark, early days of using LiPos for RC. Days when an 8C pack was an expensive miracle, and to get more than 1300mAH you needed to run packs in parallel. Days when the concept of balance charging was just starting to take hold among enthusiasts, and those who did balance their packs used external balancers after charging with their non-balancing chargers. Days when LiPo fire reports seemed like an almost daily occurrence.

Back in those days a very smart gentleman named Fred Marks (who went on to found FMA Direct and designed the excellent Cellpro series of chargers) wrote a disposal document for Kokam, one of the early high-end LiPo manufacturers. In this document he recommended disposing of the batteries in salt water. BUT, and this is a very big BUT, the document also specified that the envelope of the cells needed to be cut open so the salt water would get inside the pack and neutralize the electrolyte.

Slashing the cell to allow the salt water to neutralize the electrolyte is an effective way to dispose of a LiPo battery. BUT, and this is an even bigger BUT, slashing the cells of a charged LiPo battery is dangerous, as an early RC experimenter found out the hard way. The battery essentially exploded in his face and he was lucky to escape serious injury.

Because of the danger of slashing the cells, Fred Marks no longer recommends using the salt water bath with cell slashing. And he's always been adamant about the fact that a salt water bath without cell slashing is worse than useless (because the cell tabs will dissolve long before the pack is fully discharged). So, there is no good reason to use a salt water bath to dispose of LiPo batteries.

So, what is the safest way to dispose of LiPos? Enter the humble incandescent 12 volt automobile taillight bulb. If you have any skill at all at soldering (and you'll need it anyway if you do anything with electric RC) it's very easy to solder some wire to the contacts of a 12 volt automobile taillight, add whatever your battery connector of choice is to the other end and insulate it with electric tape or heat shrink. To dispose of your battery, just plug the battery into the taillight, put it somewhere where it's safe (I use the holes in a cinderblock with a plastic baggie full of sand above - if the battery blows the baggie will melt and the sand will pour over the battery) and leave it until the bulb goes out. Then leave it for some hours more, check the voltage to make sure the battery is completely discharged, cut of the battery connector, strip the wires and twist them together. Then dispose or recycle the now completely safe battery. A single taillight bulb will work for up to a 3S pack of any size, use two taillights in series for 4S or more.

Hopefully I have dispelled the myth of salt water LiPo disposal, and I hope that this helps people who are looking for a safe way to dispose of their LiPos.
 

rcspaceflight

creator of virtual planes
#2
I am extremely grateful for this information and hopefully this thread gets sticky-ed!

I have two 3S batteries and a 2S battery that I want to dispose of, but just haven't gotten around to yet. (The 3S's are currently outside in a military ammo box. The 2S isn't damaged other than a bad factory connection.) Although the 2S might need a different method all together. It just cuts out once in a while last time I flew with it. Maybe the 12volt light bulb would work for it.

Anyways. I will not be using the salt water method, but will be using a 12volt light bulb to drain them.

Thanks again for the warning.
 

engineer

Senior Member
#5
Not to be rude, but I will need some citation before considering using this method, which as you state is likely to generate a fire near my home. Manufacturer recommended disposal places more liability on them than you. If you are uncomfortable disposing of your batteries, let a company who is trained do it, as frogman suggests.

There are several other points I would pose in response, but not being a chemical engineer, I will hold off until I can speak with authority.
 

stay-fun

Helicopter addict
#6
I have heard more often that the salt water method is not the way to go. And indeed, if it's all just about discharging the battery, why not use the leads and the bulb as the TS describes? Makes a lot more sense than fiddling with salt water. And indeed if you don't open the battery, it won't work. But the battery will explode if you open it...

I see material for an episode here! The FT crew could take a (small!) battery, discharge it completely to 0V, and then puncture it. See if it explodes. Then do the same with a battery at e.g. storage charge, or even "depleted" (3V/cell), which will result into fire.

Gonna be one of the "don't try this at home" episodes! :applause:
 

Foam Addict

Squirrel member
#7
Ugh, IDK about empty lips, but 3 months ago, when I was still loyally following the real salt water disposal method, I accidentally over charged the outer cells of a 2200 3s pack to 6.2 volts per cell. I had my salt water bucket ready, but the moment I slit the cell casing the battery shot a jet of flaming gas into my face, singing off my eyebrows and mildly burning my skin. I dropped it in the water, but that only seemed to intensify the reaction. Thankfully I had a bucket of sand nearby, and that starved the fire pretty well, but it still smoldered for some time.

I agree whole heartedly with ace, please don't use the salt water method, and don't ever store, charge, or discharge batteries unattended.
 

stay-fun

Helicopter addict
#8
holy crap...

I slit the cell casing
Dude...

the battery shot a jet of flaming gas into my face, singing off my eyebrows and mildly burning my skin. I dropped it in the water, but that only seemed to intensify the reaction. Thankfully I had a bucket of sand nearby, and that starved the fire pretty well, but it still smoldered for some time.

I agree whole heartedly with ace, please don't use the salt water method, and don't ever store, charge, or discharge batteries unattended.
Were you wearing safety glasses? Man I thought everybody knew not to puncture lipo batteries...
 

Foam Addict

Squirrel member
#9
You were, according to the original article, supposed to slit the casings to allow the salt water to neutralize the battery.
Yes I was thankfully, as well as leather gloves. :)
 
#10
I work at a electrical recycling facility and my advice is just bring your retired batteries to a recycling facility or like frogman mentioned earlier, a place like radioshack. Lipo batteries are very dangerous when fully charged and I would not recommend anyone to slash open cells, even when they are fully discharged. We store them like they were explosives, the are stored in plastic barrels filled with something that looks like packing beans, it's called vermukulitt and doesn't ignite at any tempratures. And the barrels are stored in a container far away from any buildings. If there were a lipo fire, it's almost impossible to extinguish. The only thing that works well to put out a lipo fire is copper powder.

So please don't risk your health because of a lipo battery, just hand them over to someone who know what to do with them.
 
#11
Just to be clear - NO ONE is recommending slashing cells in this thread. The discussion about slashing cells was just a historical aside to attempt to explain where the salt water disposal recommendation originated. My purpose in starting this thread is to put the final nail in the coffin of salt water disposal.
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#12
Ace,

I would ask that you get some pictures together, and rewrite this as an article in that section of the website.

In the mean time I'll be making this a sticky.
 

rcspaceflight

creator of virtual planes
#13
I stopped by Radio Shack today to buy the stuff to make a LiPo discharger. I bought gator clips to make it universal and bought a 20W 12V halogen lightbulb. I'm assuming that the slower you discharge the LiPo the safer it is. But I didn't want to go with a tiny 12V 650mah LED.

I just shoved the bulb into some speaker wire and used the screws on the gator clips to mount the wire. I need to either get the gator clips sleeves on or make sure they don't touch.
lipo discharging.jpg

Edit: Oh, and I plan on just hooking this up to a LiPo and keeping it in my military ammo box. Probably over night, outside, and then do the recommendation of plugging the battery into it's self. I'm not sure what to do with it after that. Maybe I'll get a second ammo box to store my "dead" batteries until I have enough to recycle/dispose.
 
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#14
Safety above all. Definitely good sticky material, thanks Fred.

Ok, after a bit of research, I found a manufacturer document about disposal. It does mention both methods.

0) If any part of the recommended disposal detailed below makes you uncomfortable, allow a qualified company to dispose of it for you (as suggested, RadioShack or perhaps your local hobby shop).


1) Salt water disposal is recommended by manufacturer when total voltage is below 1V. This is because electrolysis of salt water occurs around 1.2v, so there should be a safety margin there.[2]

2) If any of the cells are physically damaged, do not discharge. There is considerably more fire hazard if the cells have any damage to their container.

3) Discharge battery in a fire-safe location by use of automotive lightbulb for 24 hours (You could bury in sand, or use a cinderblock structure away from anything flamable). After verifying that the total voltage is below 1V, submerge battery in salt water bath for 2 weeks. At this point, it is landfill-safe. (Instructions do say to score the cells, I am not personally comfortable reccomending that action after hearing some stories in this thread).

Sources:
http://www.rctoys.com/pdf/thunder-power-disposal-of-old-damaged-lipo-batteries.pdf
[2]http://en.wikipedia.org/wiki/Electrolysis_of_water
 
#15
But I didn't want to go with a tiny 12V 650mah LED.
In any case, using a LED is not a good idea. LEDs stop conducting below a certain voltage (actually there will be a tiny leakage current, but for our purposes they're essentially not conducting) so you'll never get the battery fully discharged if you use a LED. That's why I specified an incandescent taillight bulb.
 
#16
3) Discharge battery in a fire-safe location by use of automotive lightbulb for 24 hours (You could bury in sand, or use a cinderblock structure away from anything flamable). After verifying that the total voltage is below 1V, submerge battery in salt water bath for 2 weeks. At this point, it is landfill-safe. (Instructions do say to score the cells, I am not personally comfortable reccomending that action after hearing some stories in this thread).
If you are not scoring the cells (which is a BAD IDEA) I see no point in doing the salt water bath vs just leaving it connected to the taillight discharger for a longer time. A discharged battery is a discharged battery, whether it was discharged using a taillight or a salt water bath. As long as a voltmeter hooked up to the battery shows no voltage, the battery is fully discharged and no salt water bath is going to help.

The recommendation to use a fireproof container or bucket of sand is an excellent one. Although it is very unlikely that a LiPo battery might catch fire when doing a taillight discharge, it is not impossible, and the consequences can be very dire. So always ensure that if the battery does go up in flames you, your loved ones and your property are protected. This also applies to charging - charging is the most dangerous time when LiPos are concerned. I also charge my LiPos in the cinderblock holes I use for discharging.
 

rcspaceflight

creator of virtual planes
#18
Wait, the two 3S batteries that I want to discharge to make safe are damaged. Should I still use the halogen bulb to discharge them? Like I said earlier, I am going to do it inside of a military surplus ammo box that I'm going to leave outside while it discharges. (I may just leave it for 3 days before disconnecting.)

How do I make a damaged battery safe? Or is there no guaranteed way? Do I just use extra precautions when discharging? I don't think either battery is so damaged that it would cause an issue, I just want clarity.
 
#19
Although a taillight bulb is a gentle way to discharge a pack (2-3A for a 30W bulb on 3S) when compared to the discharge rates seen when flying, there is still a non-zero chance that the pack will misbehave and "vent with flames" while the discharge is in progress. If the ammo can is open (closed ammo cans with burning LiPos essentially become a bomb - don't store LiPos in a sealed ammo can!) and far away from anything flammable, the chances of any serious problems become very remote.

One thing I would make sure of is to check the pack voltage before the discharge. If it's 0, it probably means that there's a disconnect in the wiring, so discharging just won't work at all and you'll have to let the professionals handle it.