# Batteries and the law of conservation of energy
**URL:** https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082
**Category:** Factual Questions
**Created:** [August 12, 2010, 8:39pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082 "2010-08-12T20:39:35Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)
#### Post date: [August 12, 2010, 8:39pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/1 "2010-08-12T20:39:35Z")
OK, consider a fully charged car battery (lead-acid). Now pour out all the acid. The battery is no longer charged. Where did the energy go?
Consider a dry cell (AA, C, D, etc) or any rechargeable battery. As it sits unused, power is lost. Where does it go?
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### Author:  [@Lemur866](https://boards.straightdope.com/u/Lemur866)
#### Post date: [August 12, 2010, 8:43pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/2 "2010-08-12T20:43:12Z")
The acid is still there, poured on the ground. Eventually the acid will react with stuff, and there goes the acid.
As for a battery that’s just sitting there, the discharged energy turns into heat. Except it’s only a little bit of heat, so you don’t notice that the battery is hot.
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### Author:  [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)
#### Post date: [August 12, 2010, 8:45pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/3 "2010-08-12T20:45:16Z")
Yes, but acid != energy, is it?
How about if you disassemble a new zinc-carbon battery? Where would the energy go in that case?
Regarding the unused battery, does the battery’s internal resistance have anything to do with it? Do longer lasting rechargeables have a lower internal resistance?
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### Author:  [@Giles](https://boards.straightdope.com/u/Giles)
#### Post date: [August 12, 2010, 8:52pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/4 "2010-08-12T20:52:08Z")
The energy is chemical energy. You get energy by burning petrol in the engine of your car. If you siphon the petrol out of the tank, where does the energy go? It’s still there, in the petrol outside the car. Similarly, the energy of a battery is in the chemical components of a battery.
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### Author:  [@yabob](https://boards.straightdope.com/u/yabob)
#### Post date: [August 12, 2010, 8:52pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/5 "2010-08-12T20:52:20Z")
In both cases, the electricity is produced as the result of a chemical reaction which takes place in the battery. The energy is stored in the atomic bonds of the substances involved in the reaction. If you disassemble it, they stay that way. No more a violation of conservation of energy than a chemical reaction which produces heat or an explosion.
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### Author:  [@Keeve](https://boards.straightdope.com/u/Keeve)
#### Post date: [August 12, 2010, 8:53pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/6 "2010-08-12T20:53:01Z")
I think you might be confusing energy with potential energy. (or maybe I’m the confused one)
Consider this: You battery doesn’t really have any energy. It just has a bunch or chemicals which will start producing energy after you complete a circuit. It’s like a match, which is just chemicals until you strike it and stare a very energetic fire.
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### Author:  [@yabob](https://boards.straightdope.com/u/yabob)
#### Post date: [August 12, 2010, 8:58pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/7 "2010-08-12T20:58:17Z")
BTW, the wiki articles on these battery types give you the chemistry involved:
> **[Lead–acid battery | Electrochemistry](https://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery#Electrochemistry)**
>
> In the discharged state both the positive and negative plates become lead(II) sulfate (PbSO4), and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water.
> **[Zinc–carbon battery | Chemical reactions](https://en.wikipedia.org/wiki/Zinc%E2%80%93carbon_battery#Chemical_reactions)**
>
> In a zinc–carbon dry cell, the outer zinc container is the negatively charged terminal.
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### Author:  [@johnpost](https://boards.straightdope.com/u/johnpost)
#### Post date: [August 12, 2010, 9:02pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/8 "2010-08-12T21:02:30Z")
the energy is in the difference in electrochemical potential of the chemicals on the battery plate material. put in more electrolyte and you can retrieve that energy.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [August 12, 2010, 9:38pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/9 "2010-08-12T21:38:03Z")
> [@](#):
>
> Consider a dry cell (AA, C, D, etc) or any rechargeable battery. As it sits unused, power is lost. Where does it go?
When the question is “where did the energy go”, the answer is almost always “heat”. In fact, the first question in the OP is the first time I’ve ever seen the question asked where that wasn’t the answer. It’s still the answer for the second one, though.
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### Author:  [@jrepka](https://boards.straightdope.com/u/jrepka)
#### Post date: [August 13, 2010, 4:52am UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/10 "2010-08-13T04:52:30Z")
> [@Running\_with\_Scissors](#):
>
> OK, consider a fully charged car battery (lead-acid). Now pour out all the acid. The battery is no longer charged. Where did the energy go?
The energy in a lead acid battery is stored in the potential difference between the reduced lead and the lead oxide. If you pour out the acid, there is still a potential difference between the plates; you’ve just removed the electrolyte, making it much more difficult for the reaction to occur.
> [@](#):
>
> Consider a dry cell (AA, C, D, etc) or any rechargeable battery. As it sits unused, power is lost. Where does it go?
In a dry cell energy bleeds off into the air; it’s a slow process but as Lemur866 said, it heats the reactants and ultimately, the air around the battery…
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### Author:  [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)
#### Post date: [August 13, 2010, 7:33pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/11 "2010-08-13T19:33:55Z")
> [@jrepka](#):
>
> > [@](#):
> >
> > Consider a dry cell (AA, C, D, etc) or any rechargeable battery. As it sits unused, power is lost. Where does it go?
>
> In a dry cell energy bleeds off into the air; it’s a slow process but as Lemur866 said, it heats the reactants and ultimately, the air around the battery…
So if the battery was sealed in a vacuum it wouldn’t lose any energy? That doesn’t sound right. I actually think it’s the battery itself that is heated.
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### Author:  [@jrepka](https://boards.straightdope.com/u/jrepka)
#### Post date: [August 13, 2010, 8:05pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/12 "2010-08-13T20:05:45Z")
> [@Running\_with\_Scissors](#):
>
> > [@jrepka](#):
> >
> > In a dry cell energy bleeds off into the air; it’s a slow process but as Lemur866 said, it heats the reactants and ultimately, the air around the battery…
>
> So if the battery was sealed in a vacuum it wouldn’t lose any energy? That doesn’t sound right. I actually think it’s the battery itself that is heated.
I think that’s what I said – the reactants heat up (which heats the battery itself) and that heat bleeds off to the environment. If the battery is sitting in a drawer, the air in the drawer and whatever the battery is touching will be heated; if the battery was orbiting Pluto it would still lose energy by the same process but it would have to give up all of its heat by radiation.
My point was that, to the extent that energy is conserved, energy is conserved here. Chemical potential energy is converted into heat and heat moves by whatever is the most efficient process from regions of higher temperature to regions of lower temperature.
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### Author:  [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)
#### Post date: [August 14, 2010, 3:45pm UTC](https://boards.straightdope.com/t/batteries-and-the-law-of-conservation-of-energy/550082/13 "2010-08-14T15:45:48Z")
Yeah, sorry, I read it too fast and skipped over the part about it heating the reactants.