Reversing polarity on a battery?

In summary, the conversation discusses the possibility of recharging a completely dead car battery with reversed polarity. While the original questioner believes this is impossible due to the internal chemistry of the battery, another person presents a personal experience where they were able to charge a homemade lead-acid battery with reversed polarity. The conversation concludes that while this may be possible for some batteries, it is not recommended as it can lead to reduced performance and potential safety hazards.
  • #1
Evil Bunny
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A colleague of mine (who I trust is telling me the truth) just told me that he has seen a completely dead battery (a car battery) recharged so that the polarity was reversed from its original configuration.

I'm not well versed on the inner workings of a battery, but I thought the chemistry inside the cells determined the polarity...

Can someone explain this?
 
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  • #2
You are right. Your friend is wrong. To change polarity of a traditional electrochemical voltaic battery cell, you would have to change the internal materials around. This is kind of pointless, as it is easier to just switch the orientation of the battery if you want to switch polarity.
 
  • #3
A completely dead battery that has been dead for years... If you put the charger on it backwards, would it not hold the charge for a short time? Is it impossible?

I'm asking because I don't know. He insists he's seen it and he usually knows what he's talking about. I would be surprised if he was making it up.
 
  • #4
I think he may be right. When I was a boy I made a primitive rechargeable cell simply by immersing two lead plates in sulphuric acid. I charged the cell by connecting across the plates a pd of more than 2 V from an external source. One of the plates acquired a brownish tinge from the lead dioxide deposited on it, and the cell did store a little energy.

Since the plates started out identical, which one became the positive depended solely on which way round I connected the charging pd. Now in a proper commercial lead-acid battery, the plates are different, though, I think both are lead-based. One is prefilled with lead dioxide, I believe. So the battery only stores a decent amount of energy if it's charged one way round, but I wouldn't be surprised if it stored a little when completely discharged and then charged the wrong way round.

[I wouldn't do experiments on a proper lead-acid battery: its internal resistance would be so low that accidental short-circuits could be disastrous.]
 
  • #5
chrisbaird said:
You are right. Your friend is wrong. To change polarity of a traditional electrochemical voltaic battery cell, you would have to change the internal materials around. This is kind of pointless, as it is easier to just switch the orientation of the battery if you want to switch polarity.

His friend is correct. The plates of a discharged lead acid battery (like the car battery his friend referred to) are both lead sulfate, there is nothing to switch around. A fully discharged lead acid battery can indeed be charged in either polarity.

It won't necessarily work as well, however. When charged, one plate becomes spongy lead, while the other becomes lead oxide, with different reactions occurring on each as the cell charges and discharges. Some batteries may have the plates of each cell be differently shaped to accommodate the changes in volume or give one side more surface area, leading to reduced performance when charged backwards. They might also use different alloys or additives for the anode and cathode plates. And this is all for lead acid batteries, not all battery chemistries allow this.
 
  • #6
I don't know that much about batteries, but what I have read shows that cjameshuff is correct. Once discharged, both plates in a cell of a lead acid battery are Lead Sulfate, PbSO4. Unless there is something very different between the plates, then reversing the polarity should work.
 
  • #7
Thank you for the correction. I did not know that car batteries had identical plates when totally uncharged. It looks like I will have to read up on it more. :grumpy:

So I think the best summary is that batteries with different-material electrodes cannot be reversed in polarity upon recharging, but batteries with same-material electrodes can be.
 

1. How does reversing the polarity on a battery affect its performance?

Reversing the polarity on a battery can cause damage to the battery and its connected devices. This is because the flow of electricity is disrupted and can lead to short circuits or overheating.

2. Can reversing the polarity on a battery cause explosions or fires?

In some cases, reversing the polarity on a battery can lead to explosions or fires. This is especially true for lithium-ion batteries, which can be volatile when exposed to incorrect polarity.

3. How do I know if I have reversed the polarity on a battery?

The most obvious sign of reversed polarity on a battery is if the device connected to the battery does not work or is not receiving any power. Additionally, you may notice unusual smells or the battery may feel warm to the touch.

4. Can I fix a battery that has had its polarity reversed?

It is not recommended to try to fix a battery that has had its polarity reversed. The damage may be irreversible and attempting to fix it could be dangerous. It is best to replace the battery with a new one.

5. How can I prevent accidentally reversing the polarity on a battery?

To prevent accidentally reversing the polarity on a battery, always make sure to double check the positive and negative connections before connecting the battery. Additionally, make sure to follow the correct polarity when replacing a battery in a device.

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