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Author Topic: How efficient is a rechargable battery?  (Read 7104 times)

Offline thedoc

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How efficient is a rechargable battery?
« on: 19/06/2012 18:08:54 »
Hi, Naked Scientists.

My name is Gabrielle Keighley and my dad has a question that he was wondering that you could answer please.  He recently bought some rechargeable batteries for some of our toys and as he was doing the first charge, we wondered about the efficiency of recharging batteries.  Is it an efficient process regarding the amount of power or energy going into the battery as compared to the amount of power that is stored and used?

Cheers from the Land of Oz.

We love the show.  Thank you.
Asked by Gabrielle Keighley


                                        Visit the webpage for the podcast in which this question is answered.

 

« Last Edit: 19/06/2012 18:08:54 by _system »


 

Offline Phractality

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Re: How efficient are rechargeable batteries?
« Reply #1 on: 01/04/2012 12:52:18 »
If you use the batteries within a few days after recharging, you get back most of the energy you put into them. It's not 100% because the batteries get warm while charging, and that warmth is lost to the surroundings.

If you don't use them for a month or two, they will lose all their charge due to internal leakage. So that makes them 0% efficient. You should not use rechargeables for smoke detectors because they will need to be recharged every month or two, whereas most non-rechargeables can power a smoke detector for at least a year.

If you store a bunch of batteries for emergencies, they should be non-rechargeable.

Hopefully, someone will soon invent a rechargeable battery that doesn't have to be recharged so often.
 

Offline syhprum

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Re: How efficient are rechargeable batteries?
« Reply #2 on: 01/04/2012 19:54:45 »
How does the charge retention of reachargable batteries comprae with capacitors?, there was some worry after the war that the capacitors in unexploded bombs and mines might retain their charge for several years, was this misguided ?.
 

Offline David Cooper

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Re: How efficient are rechargeable batteries?
« Reply #3 on: 01/04/2012 20:37:27 »
There are quite a few kinds of rechargeable batteries now designed to be able to hold their charge for months, and they come charged rather than flat too, though they still do lose charge over time and won't necessarily perform well straight out of the packaging.

Capacitors do seem to hold their charge for a long time - a flashgun put away for months may be able to release a full flash after all that time even if the batteries were taken out of it when it was stored, but I don't know what would happen if it was left for years. Perhaps someone will try it and answer in this thread...
 

Offline Phractality

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Re: How efficient are rechargeable batteries?
« Reply #4 on: 01/04/2012 21:38:39 »
Electrolytic capacitors don't hold their charge as well as paper or mica capacitors. I think the latter can hold a charge for many years, provided the voltage is not sufficient to ionize the surrounding air.
 

Offline Geezer

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Re: How efficient are rechargeable batteries?
« Reply #5 on: 02/04/2012 01:17:52 »
Some types of capacitors can even "self-charge", which can be very dangerous.
 

Offline techmind

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Re: How efficient are rechargeable batteries?
« Reply #6 on: 04/04/2012 23:32:59 »
The types of general-purpose rechargeables you use in toys and things are normally NiMH, and are somewhere around 80% efficient (you get back about 80% of what you put in) - assuming you have a good quality charger which terminates the charge when it should. If you put excess charge in then you won't get that energy back AND it'll prematurely wear-out the batteries.
 

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Re: How efficient are rechargeable batteries?
« Reply #6 on: 04/04/2012 23:32:59 »

 

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