I found a small puddle under battery after charging it


I just finished assembling a battery with Lishen LR2170SD and after charging it 100% and taking it off the charger i found a small puddle under it. It had no color and a nasty smell. I presume it’s lithium.

The battery is not for me so i’m worried about safety. I found a cell which had liquid on negative pole and started taking off the nickel strip.

Unfortunately i couldn’t find any hole. I tought that maybe the spot welding made a hole and liquid came out. I took out the cell entirely and there is no sign of damage. I looked to the nearby cells and no sign of wet cells.
I intend to replace the cell and just for curiosity test the capacity of the suspicious cell. It’s really concerning to me because i am worried about batteries taking fire. It’s the first time when i encounter something like this and it’s the reason why i use quality cells.

Do any of you had similar experience ? What did you to do avoid problems like this ?




Do not charge it or discharge it. Keep it away from heat or flame.

That smell is the toxic and flammable “electrolyte” from inside the cell. It is made of organic solvents and lithium salt. That stuff is nasty and you must carefully clean up all residue. Do not touch it or breathe the fumes.

If you accidentally ignite the electrolyte the cell can catch fire and possibly burst.

The cell is ruined and cannot be used. Wrap it in paper towels, place it in doubled zip lock bags, and recycle it properly. Then thoroughly wash your hands and anything that liquid touched.


Well, something went through the metal can. :slightly_smiling_face:
You might have burned your way through the pre-weakened venting ring on the bottom, opening up the cell.

You must NEVER weld on the ring, preferably not next to it either, and any solid nickel strip used on the bottom of bottom-vent cells will interfere with proper operation of the vent. This can cause the cell to burst instead of simply venting in case of a problem.

You can certainly decide to take the risk of that happening. Just be aware that this risks exists.

Never weld in the bottom center of any li-ion cell either as that’s where the spot welding of the negative tab for the cell is done.


That should be the problem, the weaker ring. I couldn’t explain myself how i could make a hole in the can, the welder is not that strong.

I assembled like 400 cells and probably a lot of them have welds on the ring. It is a big project and i am really concerned now because of the possible repercussions. What would be the best thing to do now ? Charge, discharge battery, check for leaks, then flip over the battery and do it all again ?

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Ah dude this suuuuucks. I think you need to replace all cells with welds on the outer ring.

This is one of the only bottom vented cells ive seen used in esk8, so don’t kick yourself too much for this error but god damn this is a shitty situation.


Wow. Such a bad luck man… I really feel your pain. It would never come to my mind that this is an option to happen. :frowning_face:


I don’t know.
Until I can see multiple examples of how the established pack manufacturers like Dewalt, Milwaukee, Dyson, and others connect bottom-vent cells I just don’t have any recommendations other than don’t cover the bottom of bottom vent cells and definitely don’t spot-weld them.

I know doesn’t help you at all though. :slightly_smiling_face:
Even if you can cycle that pack a couple of times without detecting leaks (realize that some leaks could be missed) some cells could have damaged vent rings and open up later as the internal pressure goes up/down as the pack is used.

Replacing cells that have welds on or near the rings can help prevent damage to the rings but still leaves the vents blocked. Do you accept the additional risk that brings? The risk can’t be quantified so all we can say is it’s worse to block the vent than to have the vent unblocked. If this unknown additional risk is acceptable then I guess you just need to replace all affected cells.

But my personal recommendation, due to there being no good examples of how to use bottom vent cells in a spot-welded pack, is to err on the side of caution. Unfortunately that means I recommend not using those cells at all in a welded pack. Carefully salvage the ones you can, test them thoroughly, and use them with a cell mounting system that doesn’t risk damaging the rings or apply pressure to the center of the bottom of the cell.

Some might say I’m being too cautious here. But this is personal safety we’re talking about and if someone asks me about this I will always err on the side of safety and lower risk. Each of us can choose the level of risk we want to take though.

I wish I had something cheerier to say. I’m sorry you’re stuck in this really crappy situation.


this scared me a bit, I just ordered a bunch of Lishen LR2170LA cells with full intentions to spot weld them into a flat pack, should I not weld these cells? how else can I get them into a flat pack within my dimension constraints?

Those aren’t bottom vent, I also have some of those for a pack

Normal precaution should be taken for the negative side though avoiding 3mm circle in center where internal weld is


is there any product has used this particular cell in spot welded fashion?

I haven’t seen one yet but that doesn’t mean much. Until I see multiple images of packs from established pack makers (not small China assemblers with no worries about liability!) using bottom vent cells, and seeing how they do it, I cannot recommend using these cells if the bottom is being welded or even just blocked.


yea, we need to see how the big guys are doing first before we try to do the same


I also have some bottom vent cells I’ll be using for an E-Bike pack very soon. (These are BAK 18650 2900mAh ones)
They will definitely be spot-welded and I’ve thought of something to do that safely.

Adding a fishpaper ring or maybe even better the dot from the middle on the negative end of the cell will keep the no weld area and especially the bottom vent free of welds.

This should be safe right?

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Well, i found a document about NASA’s approach to battery building and thermal runaway testing, including bottom vent cells.

I extracted some valuable information both good and bad regarding our methodolgy of assembling batteries. I don’t want to bias you by my findings so i let you read the document than we’ll discuss what changes can we make to improve our batteries.


Haven’t finished reading it completely yet but wow this must have been a fun test to do

Very comprehensive, this is like stuff I’d see at work. Some really interesting designs in here.

Using G10 is an interesting idea

Bottom vent cells, that is intresting. Wasn’t even aware that was a thing.
Might be able to bond the cell on top side (both plus and minus) then without having to consider vent holes in the bussbar geometry. Designing a modular pack at work atm that is bricks of 14S6P, stackable to a 1000V. So this is really intresting for me :smiley: I have to do more research.


I think tesla is doing the fuse wire thing on the negative shoulder of the battery.
I have the same idea of modularity with modules consisting of 13s7p but meant to be wired in parallel. I made 4 of them and they can be completely wired in parallel including every cell group.

Tesla bonds on top side, both plus and minus on all new packs :slight_smile:
(theres a whitepaper on why thats good but can’t seem to find it atm)


These guys do it too. Here is a screen shot from the video in the article. I feels kinda unsafe to weld on the edge of the cell, but on the other hand it makes mass producing the packs a whole lot quicker. They also seem to be using very cool nickel that is over molded with plastic, so it stays in shape and is one big sheet.