Angry in the Great White North

One of my readers, Iron Oxide, posted this comment on my discussion of exploding counterfeit batteries:

We had an incident at my work because of exploding batteries. A 9V blew up on a desk imbeding powder in a couple of books and sending parts flying. It was reported as sounding like a .22 going off. It was a sufficiently serious incident that it was reported as a near miss for our health and safety commitee and when the manufacturer couldn't explain how it happened we switched to a different make of batteries. I'm going to try and track down the pictures...

The pictures have arrived, and they are fascinating. I've cropped, resized, or enlarged the photos from the originals format sizes.

I'm on the Health and Safety Committee at my workplace, and I can tell you the decision to make a report is not a trivial one. But with the way the contents of the battery was so powerfully discharged that it was embedded inside of the nearby book makes it clear that it required reporting. Imagine getting an eyeful of that discharge.

Look at the third picture. It shows how a 9V battery is constructed. It is six 1.5V batteries connected in series, and then enclosed in the square outer casing. That means that when it comes to venting a buildup of hydrogen gas, each of the 1.5V batteries needs to be constructed with the venting mechanism I described in the previous posting. The outer casing of the 9V battery does not directly enclose electrolyte, but is just a frame to hold the 1.5V batteries together, so venting from there is simpler.

So what happened? Though working off a picture is hardly conclusive, you can see several hints that strongly suggest the root cause. I've labelled the key elements. Look at this cross-section as I describe what I think I'm seeing.

1. This is exposed anode and cathode material. It is contained in a cavity above the plastic grommet.
2. This is the anode current collector, showing that the failure definitely occurred at the negative end of this particular cell.
3. This is the crimp line that indicates the location of the plastic grommet. It shows that the casing failed above the grommet.

What should have happened is that a vent in the plastic grommet ought to have opened when too much pressure built up in the main cavity. The vent would have released the hydrogen gas out of the cell and from there into the 9V battery casing and then to the outside. Once the vent had opened, the electrolyte would have slowly leaked out.

The point is that the cell is designed to fail without coming apart at the seams. We ought not to be able to see the current collector or the anode and cathode material.

But since we can, and because there was definitely a violent explosion, the source of the failure seems clear. The plastic grommet did not vent gas. The buildup of gas above the grommet led to a violent explosion, so violent that not only was the bottom of the battery from the grommet on down blown off, that portion of the casing struck the bottom of the outer 9V battery casing with so much force that it was dislodged along two sides. And still there was enough kinetic energy left that a mix of anode paste, cathode paste, and highly caustic electrolyte was fired out to embed itself in the nearby book.

Now why did the plastic grommet fail to vent gas, even as the pressure built to such high levels? I'm going to speculate here, but I'm going to suggest that the plastic grommet lacked any venting mechanism whatsoever. This is characteristic of a counterfeit battery, since counterfeits are known to fail violently like this for lack of proper venting. A counterfeit needs to be constructed as cheaply as possible so as to undercut the legitimate products in terms of price. Using a plastic grommet without a venting assembly no doubt significantly reduces the unit price of the fake battery, increasing profit for the counterfeiters.

At cost of potentially taking out someone's eye.

As Iron Oxide originally wrote, when the battery failed, it sounded like a .22 being fired. Actually, the comparison makes sense. Gas expands in an enclosed space -- bullets or batteries -- same thing.

I'm surprised that the Health and Safety report was so inconclusive. It might be that I'm wrong, and that the plastic grommet did have a venting mechanism, and that its failure to open is truly a mystery. But knowing what I know now, I would certainly have specifically checked the grommet to confirm its construction. A Health and Safety report requires a root cause for the incident to have been determined in order for the report to be complete. It would be interesting to have a Health and Safety report determine that counterfeiting is a serious risk to the health of workers.