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Author Topic: Why does manipulating dead batteries bring them back to life?  (Read 3028 times)

Greg Turner

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Greg Turner asked the Naked Scientists:
   
Why is it that when your remote control is losing power, you can roll the
batteries around with your finger, it works again?

Greg Turner
Victora, British Columbia

What do you think?


 

Offline lightarrow

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Why does manipulating dead batteries bring them back to life?
« Reply #1 on: 12/04/2009 17:37:47 »
Greg Turner asked the Naked Scientists:
   
Why is it that when your remote control is losing power, you can roll the
batteries around with your finger, it works again?

Greg Turner
Victora, British Columbia

What do you think?
Well, I didn't know it. However, I can assume that you help the chemicals diffuse and dissolve; during the discharge chemical reactions happens and if the chemicals cannot diffuse from one semi-cell to the other (or combine between them), the reactions and so the electricity production, is slowed down.
 

Offline graham.d

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Why does manipulating dead batteries bring them back to life?
« Reply #2 on: 12/04/2009 19:01:53 »
I don't know the answer to this, but I will have a guess. I assume you mean the action of twiddling the cells in situ. I have noticed this effect too. It is usually in items which have a relatively high current draw like a torch. I think it is simply to do with making a better electrical contact though the mystery is why this has such a big impact only when the batteries get old. I suspect that there may be some oxide build up on the battery terminals, or the metal in contact with the battery terminals, that is thin enough to be electrically broken down and, when the available current flow is sufficient, it can sustain this state. Twiddling the batteries can scratch away some of this oxide and the current flow restored for a time but limited by the batteries high internal resistance (which goes up rapidly as the batteries run out of charge). I have a suspicion that not all types of batteries will behave this way; some do not degrade so gradually as they run out of charge. I would bet that if both the battery terminals and the contacts in the equipment were gold plated, you would not see this effect at all.
 

Offline techmind

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Why does manipulating dead batteries bring them back to life?
« Reply #3 on: 13/04/2009 21:49:40 »
I would guess that the answer lies in the remote-control circuit having some specific threshold voltage (and current-availability) above which it will work and below which it will not.
When you first notice that the remote is not working, the batteries will have degraded to a voltage matching this threshold. The tiniest thing you do could move you back onto the right side of that threshold.
In general, you notice the range of the remote decreases, or you have to point it more directly at the TV before you get to the stage of not working at all.

Scratching through any oxide and/or pentrating any tiny grease layer presenting resistance and/or electrolytic effects could do it. Also just resting your fingers on the batteries for a while will warm them which tends to increase the voltage/lower the internal resistance for a few minutes at least...


(As an aside, note that the conductive plastic behind the buttons of a remote-control keypad degrade over time and use, so it may be better to replace the batteries sooner rather than later instead of spending weeks pushing the buttons unduely forcefully and hastening the overall demise of the handset.)
 

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Why does manipulating dead batteries bring them back to life?
« Reply #3 on: 13/04/2009 21:49:40 »

 

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