Whacking a Li-Ion battery

[Vanadium 50]

Another thread (now closed) raised the question of whether it is a good idea or not to "whack" a Li-Ion battery that is no longer working. It is not. But the reasons for it being a bad idea are kind of interesting.

(1) A modern Li-Ion battery is not a lantern battery of decades past. It has a non-trivial amount of control circuitry to control charging, discharging, dangerous/abnormal conditions, and so on.

I have never seen these use wires. PCB traces. (I have seen NiCad packs with wires) Doesn't mean they don't exist, just that I have never seen one.

If you "whack" one, you are more likely to break a trace than to reattach a wire - particularly if the wires don't exist. This will make things worse, not better.

(2) A battery that is not putting out power may not be discharged. The control circuitry may be responsible, even if the cell is "full".

(3) As these batteries age, little tendrils or dendrites sprout from the cathode. "Whack" a battery and these can break off and cause an internal short. Usually they are "too short to short" but not always. And usually the controller tries to do what it can to placed it in a safe state, but if the short is internal, there is only so much it can do.

I would estimate that the majority of work on battery electrochemistry is to keep these from forming, or at least to slow them down.

 

[Rive]

[Moderator's note: Off topic content deleted.]

Regarding whacking batteries - yep, you are right. A faulty battery is just not to be abused.

But the original topic was about a complete product, not specifically about a battery. And while 'whacking' is not really recommended, applying various forms of mechanical stress within the limits of what it could experience in normal usage might be a form of diagnostics.

Of course you need to ensure that any form of the applied stress would not exceed the 'normal' and also should be prepared for consequences.

And yes, sometimes batteries inside can explode. You need to be prepared for that too, otherwise you are no expert but just a layman whacking things.

 

[Vanadium 50]

Of course you need to ensure that any form of the applied stress would not exceed the 'normal'

People are beginning to consider this more and more in battery design. A UPS battery sitting in a rack gets "whacked" less than a cell phone battery. So one can emphasize factors other than mechanical robustness.

One can also deemphasize the number of charging cycles, which could be dozens for a UPS and thousands for a cell phone. While the electrochemistry still has a way to go, one can start to optimize it for various applications.

 

[berkeman]

After a Mentor discussion, some thread cleanup and the departure of a problematic member, the thread is reopened provisionally.

 

[Vanadium 50]

One thing I forgot to mention. There are liquid batteries in the lab. The intended market is EVs, and part of the appeal is less mechanical shock. To be honest, I am kind of skeptical that it can be made to work as hoped, but it shows people are keeping an eye on this.

 

[jrmichler]

A common cause of electrical problems is contact corrosion. While a whack can jiggle the battery contacts just enough to reestablish contact, it's better to just remove and reinstall the battery. Or even just wiggle the battery.

 

[Baluncore]

Silicone dielectric grease on the battery terminals will prevent corrosion from day one.

 

[Tom.G]

Silicone dielectric grease on the battery terminals will prevent corrosion from day one.

And before that was available, Petroleum Jelly was used (popular brand - Vaseline, available at your local drug store).

 

[jedishrfu]

I recall a coworker having battery trouble and another suggesting they turn on the lights, and the car started magically. The flow of electricity was enough to overcome the initial resistance to starting without the lights on.

In another instance, I saw a video in which an Eastern European started a fellow driver's car by taking their own battery out of the car, flipping it upside down, and placing it on the contacts to jumpstart the car.

It was a dead battery, and it was impressive that the flipping worked. it was quite frightening to think what could have gone wrong.

 

[Rive]

A UPS battery sitting in a rack gets "whacked" less than a cell phone battery.

On the other hand, a bigger battery likely to have beefier high current contacts => more whack-resistance.
Still no guarantee for crashes, though. Don't do this with cars.

Just remembered of some refurbished battery packs with DIY spot welds I came across once. Not sturdy. Spot weld better done with proper equipment and preparations.

 

[Vanadium 50]

On the other hand, a bigger battery likely to have beefier high current contacts => more whack-resistance.

I was visiting a data center and was told that a lot of the UPS were lead-acid. Clearly someone felt a different optimization point was ideal. I wouldn't disagree with the statement that a 30 minute supply that you buy works better than a 4 hour device you can't afford.

 

[Vanadium 50]

an Eastern European started a fellow driver's car by...

Why do Trabis have rear window defrosters?


To keep your hands warm when you push them.

 

[Rive]

I was visiting a data center and was told that a lot of the UPS were lead-acid.

Sure. Although there are Li-whatever batteries which can handle 10C discharge for a prolonged period, usually those are not really cheap. The same discharge is just 'business as usual' for a common LA battery.