From a little triple-A cell to a big Sears car battery… How much total energy?
Also…how long to discharge? If I put a wire across the contacts of a double-A cell, the wire gets hot…but how long until the battery is kaput? Same with a car battery: if I short the ends of the jumper cables, the cables get mighty hot…but how long till the battery is inert?
(I’m mostly curious just about double-A batteries.)
it really depends on the cell chemistry, because a cell’s chemistry determines its internal resistance. And when internal resistance is a factor, how much “energy” you can get out of it depends on how rapidly you try to extract that energy. for example, an alkaline AA might have 2200 mAh of capacity if you’re only drawing 100 mA of current, but only about 1.1 mAh if you draw 500 mA of current.
Your typical AA battery holds about 500 to 2500 milli-amp hours (mAh) of energy, depending on the battery chemistry. This isn’t exact, but you can figure a 2500 mAh one would last roughly 50 hours at 50 milliamps, or 25 hours at 100 milliamps, etc.
By comparison, a typical car battery is probably somewhere in the 40 to 50 amp-hour range (40,000 to 50,000 milliamp-hours).
It’s not a good idea to put a dead short across a battery, as the excessive current can cause the battery to overheat and possibly explode. A dead short on a AA battery is probably going to result in a current of a few amps. A dead short across a car battery will result in several hundred amps of current (and again the battery’s electrolyte might boil and the pressure could cause the battery to explode).
I googled ‘energy in an aa battery’ and got a table from the Wikipedia article on AA batteries. Looks like it’s 1800–2600 mAh for an alkaline battery at under 50 mA constant drain. I imagine there are similar tables for other batteries.
I’m not sure about the short situation because performance can get weird there.
Batteries are typically measured in “mAh” - milliampere-hours. This is integral of the discharge curve measured from full to some specified cut-off. For a typical AA NimH battery, the mAh rating might be 2,000. The total energy delivered is the mAh * the average voltage, which is around 1.2v, or around 1.4 Watt-hours.
A car battery is vastly larger, and might be in the range of 70,000 mAh (70 Amp-hours), but it’s also 12v (nominal), so the total power is something like 840 Watt-hours. Car batteries are usually sold by “CCA” (Cold Cranking Amps), which doesn’t tell you anything about their total energy storage.
It’s a complicated topic. Total battery energy is also affected by the rate of discharge.
ETA: Wow. Too slow.
There’s the kinetic energy associated with the batteries’ temperature, unless it’s at 0 K … car batteries have portions that are liquid, so there’s the energy of liquification … is it on the surface of the Earth, then there’s the gravitational potential energy … the motion of the Earth spinning, orbiting the Sun, the Sun orbiting the Milky Way, the Milky Way gyrating within the Local Group …
Maybe you mean the electrical energy stored that can be withdrawn without ripping the string fabric of the universe apart?
More complex than I had imagined!
Since an ordinary AA isn’t gonna kill me, maybe I’ll just sacrifice a couple and find out experimentally. (Not with a car battery!)
Thanks, everyone!
A shorted AA battery isn’t going to explode like a grenade, but it might pop and leak or spray very hot goo from its insides. Be careful.
How much does the battery weigh? Or rather, what is its mass? E=mc[sup]2[/sup] and all that.
Oh! Okay. I haven’t started yet, so now I might not at all. Some wisdom is best learned from paying attention to the advice of people who know more than I do!
Grin! That’s a LOT of energy! Too bad there isn’t any easy way to access it: an AA battery would power my car – not my car’s electrical system, but my whole car! – for just about the rest of my life!
I think he was asking about total energy not about externally available energy.
I think he was asking how powerful the explosion is if you do short out a high current battery like a car battery or lithiums like exploding samsungs ?
Well, I dont know why he asks here, its the capacity.
Batteries and voltaic cells like the AA and the car battery are commonly rated by their voltage, and their charge capacity. The charge capacity is useful as it allows you to know how much charging it needs… if its 2600 mAh … you need to charge it at X milliamps for Y hours, so that X*Y = 2600… so to find time, time=2600 / X.
Well to get from mAh to energy, convert that mAh to Ah if needed ( Amp hours…easy … divide by 1000 to change mAh to Ah ). Then multiply by battery voltage. Thats in Joules directly, although a common measure of explosive energy is tonnes of TNT … I’m not going to tell you how to convert…
all that is true, but different battery chemistries deliver energy differently. a lead-acid car battery can dump thousands of amps into a dead short. a carbon-zinc dry cell will sag so badly when shorted that it’ll do little other than slowly consume its case and leak.
An amp-hour times a volt isn’t a joule. It’s 3600 joules. Remember, a coulomb is an amp-second.
Which is why, incidentally, you shouldn’t put batteries in your pocket with your keys, although it’s a particularly bad idea with 9v batteries with the terminals at the same end.
Anyway, my AA battery here weighs about 25g, so, E=mc²…
repeating “E=mc^2” isn’t really contributing anything.
Actually, I didn’t know the two were different! In general, I wanted to know how much energy you can get out of a battery, either shorting it fast, with a low resistance bridge, or slow, with a higher resistance bridge. But if total energy is different, then I’m curious to know that, too!
(And I might even be saying that bit about resistance wrong. Gimme a break; I never studied electrical engineering!)
Throw in a lot of heat and resistance loss, but if I put an AA battery to a little toy electric motor, and used it to reel up a thread with a weight at the end…how far would it lift it before dying? (I grok that the difference in total energy measured would not be linear based on the weight.)
Doesn’t bother me a bit; I still think it’s funny.
