The nice thing about standards is that there are so many of them. This is very true in the world of batteries. And so it is that I’ve encountered a new (to me) genus of batteries, which I’ve christened Russian Doll.


By BrokenSphere - Own work, CC BY-SA 3.0, Link

Like the dolls, batteries in this genus are constructed from smaller batteries (okay, cells). The 12V “23A” (a.k.a A23, MN21, MN23...) battery considered here consists of eight LR932 button cells. They are used in applications like remote controls and security system sensors, where a higher voltage is required while maintaining a small package (like in the wireless door sensors of my alarm system (teardown coming)).

So what’s the problem? Out of the 20 batteries I ordered, about half were dead on arrival! See for yourself:

Under a 1 kΩ load, the bad parts read anywhere from really dead (e.g., 1mV) to weak (e.g., 11.5V). What’s telling is that all the cells in the two dead batteries I dissected measure good.

Aha! The problem is contact-related.

I’m not the least bit surprised. After all, I managed to unravel the dissected batteries using just finger power; no tools required. How manufacturers expect good contact to be maintained, especially over time and fluctuating environmental conditions, is beyond me.

That said, this battery style is made by big-name manufacturers too, like Eveready (or do they just call themselves Energizer now?), Duracell, and Toshiba. They wouldn’t stand for a 50% failure rate. Better production processes – clean cell contacts, and higher stack pressure (with perhaps a bit of compliance) – must yield a reliable product. Perhaps they even weld the cells together.

With my curiosity now officially piqued, I ordered batteries from those name brands, as well as three more far-east manufacturers. Here’s a summary of my findings:

Battery

% good
on
arrival

% good
after
thermal
cycling

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Firecracker cells…blowed up good.

 

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 Green energy, easy life.

 

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BANG!

What are firecracker cells, you ask? Once I had some good batteries in hand, I replaced all from that first awful batch I’d installed (some of which had died of course). One in particular was difficult to remove. I think it had grown a bit! Then, without warning, as I leveraged it out, it went off with a bang!!! One of the cells exploded like a small firecracker. Then, a few more cells went off. Wow. The remaining batteries are now resting in a metal enclosure awaiting disposal, and away from anything flammable! Not that I think they could combust. But…

BTW, the cells in that first set of batteries are labelled LR930, not LR932 (as all the sources I could find specify). In fact, the LR930 doesn’t even seem to exist. It makes one wonder.

Fix?

Can the defective batteries be fixed? Maybe. I’ve got one here that reads 1mV under load, but applying a bit of pressure with my probes pushes that to 20mV. No-load readings jump from 4V to 8V. Let me try something…

Okay, after applying a bit of pressure around the wrapper rim with my bench vise, readings are now 20-30mV loaded, 11V unloaded. A measurable improvement, but still closer to dead than alive.

Dissected samples of all the batteries. None are welded.

Note one Toshiba cell (separate, at the bottom of the group) has bloated and appears to want to explode. I suppose it may have been damaged when prying open the battery case (all other batteries had more solid wrappers than the first batch).

Most interesting of all though, the three name-brand batteries have corrugated spring rings as part of the stack. Aha! Designed NOT to fail. Actually, the PKCell also has a spring, yet experienced some failure. Who knows...

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Michael Dunn is Editor in Chief at EDN with several decades of electronic design experience in various areas.