- + battery change

[thirteen]

This is an odd battery question, but if a battery has been discharged to O then recharged but in a reverse of neg to pos. why can't it operate the same as before? Just an odd question.

[joestue]

i've thought about this, but only reusing the negative plates (turning half of them into positive plates) after the battery has already reached end of life.


basically the plates are optimized for the unique chemistry each faces, and positive plates will hardly survive being turned into negative plates due to mechanical strength issues and the resulting shrinkage (afaik, the active material will shrink and detach from the grids) negative grids seem to handle it just fine from what little testing i've done, but i'd imagine that they would have nearly zero capacity as the pore sizes would be all wrong. i wasn't able to get any significant capacity from them, but i didn't cycle them, just reverse charged a few negative plates to see what would happen.

[Flux]

On most batteries the plate construction is different and also there are always negative plates on the outside of a pack.

With some types of pasted plate as used in car batteries they can be reversed, it may never work well and certainly it will take some time to reach a decent capacity. I have seen it done accidentally on the starter batteries of a large generator engine and I only found it when they had a charging fault. We never found out how long previously this had happened and as the things were doing the job we left them reversed rather than risk changing them back. They started a big Cummins diesel for several years after that.

Normally I suspect things won't work out as well as that case and certainly more sophisticated batteries with Plante positives or most deep discharge cells will probably not work at all well .  Often even with pasted plates the paste and forming process is different for positive and negative so it will be far from optimum if reversed.

The basic lead acid battery is reversible but so much development has taken place over the years to improve performance that the modern cell bears little resemblance to two lead plates in a jar of acid with the spongy lead and peroxide being formed by a long charging process. The modern plates are in a form that gets you to the final state quickly and reliably without consuming huge quantities of electricity.

[thirteen]

Just was wonder what if. So thank you.

[PeterDe]

While it is not a good thing to run a lead acid battery into plate reversal, it does occur and depending upon just what the issues are that caused that cell to be weaker, it may very well recover and be useful for many years.  We every now and then will run into a 60 cell battery that was assembled with one cell or one jar that was installed in reverse, and over the years the plates obviously change polarity.  And depending upon the discharge rate applied, the battery can function satisfactorily.

With the large 2 volt VRLA cells it is common to let a cell or cells go into reversal during the test.  Very often during a formal discharge test we are looking to see if the battery will support the function that it is required for, and not just to determine its capacity as related to a published number.  These cells usually will come back around fine.

PeterD