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Author Topic: Why do unused batteries go flat eventually?  (Read 11246 times)

Jonathan Flowers

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Why do unused batteries go flat eventually?
« on: 09/01/2010 03:30:02 »
Jonathan Flowers  asked the Naked Scientists:
   
Why do rechargeable batteries (or any others for that matter) lose their charge over time, when not in use?

Jonathan Flowers

What do you think?
« Last Edit: 09/01/2010 03:30:02 by _system »


 

Offline Jonathan Flowers

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Why do unused batteries go flat eventually?
« Reply #1 on: 11/01/2010 07:54:38 »
Thanks for this.  I has assumed that it was some kind of chemical breakdown within the battery, but I don't know the mechanism, or some kind of circuit completion across the insulation in the battery, but again I don't know the mechanism.  The air circuit one really hadn't occurred to me.

My perception is that rechargeable batteries lose their charge much faster than non-rechargeable ones, and don't know why this is, but may give a clue as to the mechanism. 

I presume that batteries also lose their charge more when connected to the device as even if it's off there's more potential for a degree of current leakage.

 

Offline Bored chemist

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Why do unused batteries go flat eventually?
« Reply #2 on: 11/01/2010 09:19:00 »
There's definitely chemical degradation, even without any current flow. My guess is that the effect of flow of current through the insulation and the surrounding air is small compared to the rate of unwanted chemistry.
 

Offline Geezer

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Why do unused batteries go flat eventually?
« Reply #3 on: 11/01/2010 20:32:08 »
Thanks for this.  I has assumed that it was some kind of chemical breakdown within the battery, but I don't know the mechanism, or some kind of circuit completion across the insulation in the battery, but again I don't know the mechanism.  The air circuit one really hadn't occurred to me.

My perception is that rechargeable batteries lose their charge much faster than non-rechargeable ones, and don't know why this is, but may give a clue as to the mechanism.

I presume that batteries also lose their charge more when connected to the device as even if it's off there's more potential for a degree of current leakage.



I think BC is correct in saying that it's mostly a problem of unwanted chemistry. I seem to remember that temperature can have significant effects of self-discharge rates, which would tend to suggest the discharge is the result of a chemical reaction.

It should not make a difference if the batteries are in an appliance or not, as long as the appliance really prevents the flow of current from the battery, but some appliances go into a "standby" mode which greatly reduces the current, but there is still a slight drain.
 

Offline fas17

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Why do unused batteries go flat eventually?
« Reply #4 on: 01/02/2010 08:19:02 »
If we see the whole process and expert's advice in split equations/reactions...

Add Water and Acid to battery box/chambers (new)
do charging of battery, it becomes ready to use.
opposite ions move to respective electrode
electrons separated at higher potential
In which state Electron is at higher potential and possibility of reverse (de-charging)

Anyone demonstrate split phases of acid/water, checmial eqn...
Water of battery goes down after certain time of usage and we need to add distilled water ?
 

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Why do unused batteries go flat eventually?
« Reply #4 on: 01/02/2010 08:19:02 »

 

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