batteries are weird

owlexifry

Well-known member
when i was testing the last circuit i built, i was lazy and couldn’t be bothered taking out my usual regulated 9v supply, so i just whipped out a brand new, never used, eveready gold.
it measured a healthy 9.5v or something i think.

so the circuit was failing somewhere (solder bridging from some crap between the traces, just needed a good cleanup..)
and after removing the battery to put it away, i measured it again and it was 8.4/8.5v.
i was thinking “wtf, guess this cranked the battery pretty hard, perhaps something shorting and loading the circuit or whatever idk”

i just tested that same battery again (about 2 weeks later) and it’s back up to 9.6v.

🤷🏻‍♂️

boring story, but i’m just fascinated and confused and batteries are weird
 
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Are you testing the battery by measuring its terminals using a multimeter? I’m not technically up on this, but I think battery testers have a load in them, to see what the voltage looks like when it’s under use, which ends up being a lower number than when just connected to a volt meter.

I remember how batteries used to seem to gain voltage from resting, but also that they lost that gain almost immediately after being put into a circuit. I think (but do not know) that the chemical makeup of the battery can produce this “ghost voltage.”
 
when i was testing the last circuit i built, i was lazy and couldn’t be bothered taking out my usual regulated 9v supply, so i just whipped out a brand new, never used, eveready gold.
it measured a healthy 9.5v or something i think.

so the circuit was failing somewhere (solder bridging from some crap between the traces, just needed a good cleanup..)
and after removing the battery to put it away, i measured it again and it was 8.4/8.5v.
i was thinking “wtf, guess this cranked the battery pretty hard, perhaps something shorting and loading the circuit or whatever idk”

i just tested that same battery again (about 2 weeks later) and it’s back up to 9.6v.

🤷🏻‍♂️

boring story, but i’m just fascinated and confused and batteries are weird
Chemistry is weird. Got an A+ in physics, C in chemistry. OTOH my wife could spew out the atomic number of any element on demand....
 
Chemistry is weird. Got an A+ in physics, C in chemistry. OTOH my wife could spew out the atomic number of any element on demand....
I could do that once upon a time... had to memorize the periodic table before my Ph.D. candidacy exam - not because I was going to be quizzed on it, but because there wasn't going to be one in the room... good times... heh... yeah... heh...
 
Are you testing the battery by measuring its terminals using a multimeter? I’m not technically up on this, but I think battery testers have a load in them, to see what the voltage looks like when it’s under use, which ends up being a lower number than when just connected to a volt meter.

I remember how batteries used to seem to gain voltage from resting, but also that they lost that gain almost immediately after being put into a circuit. I think (but do not know) that the chemical makeup of the battery can produce this “ghost voltage.”
GHOST VOLTAGE?! o_O

yep - was measuring with multimeter on battery terminals.

Batteries, depending on the specific type, will often have a “recovery” time after being subjected to a good hard momentary draw. It’s a normal behavior.
i've observed this 'recovery' behaviour quite a few times.. assumed it just was a normal thing for a battery to do with moderate use, but when i saw this happen with a brand new battery i was even more perplexed about it..
 
GHOST VOLTAGE?! o_O

yep - was measuring with multimeter on battery terminals.


i've observed this 'recovery' behaviour quite a few times.. assumed it just was a normal thing for a battery to do with moderate use, but when i saw this happen with a brand new battery i was even more perplexed about it..
I was thinking it was probably due more to so LITTLE draw. Chemical reactions are like that. A large draw would start warming up the battery and the reactions and voltage would be closer to nominal. Tiny draw is like sucking too much coke out of one spot in a slurpy and it goes dry.

Yeah, I just wanted to use a slurpy analogy, lmao....
 
I was thinking it was probably due more to so LITTLE draw. Chemical reactions are like that. A large draw would start warming up the battery and the reactions and voltage would be closer to nominal. Tiny draw is like sucking too much coke out of one spot in a slurpy and it goes dry.

Yeah, I just wanted to use a slurpy analogy, lmao....
I ran into something like this at work today. Our generator while reading a solid 14v for the battery with no load, would randomly not start sometimes for the bi weekly test start that it has. When it was put under the starting load it was dropping down to 10v sometimes and other times it would only drop to 12. Resolution the cat guy spent two hours checking over everything in the electrical system to bill my company at 150$ an hour to say we need a new battery. Which of course he didnt have so they will send out a new technician to bill us for drive time and and labor to install a new battery, which I'm sure will have significant mark up. I guess it's not my money lol..
 
I was thinking it was probably due more to so LITTLE draw. Chemical reactions are like that. A large draw would start warming up the battery and the reactions and voltage would be closer to nominal. Tiny draw is like sucking too much coke out of one spot in a slurpy and it goes dry.

Yeah, I just wanted to use a slurpy analogy, lmao....
Just don't try that with a battery.

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You raise a good point. Why can't they use citric acid with a twist of lemon in a car battery? No, they have to use sulphuric acid because they want to show they're tough or something.
 
You raise a good point. Why can't they use citric acid with a twist of lemon in a car battery? No, they have to use sulphuric acid because they want to show they're tough or something.
So I threw some change into a brass dish and the cat pee'd it. When I washed it out the brass was copper plated. Did cats and coins and dishes invent electricity, batteries and metal plating? Only time traveling historians will ever know!!!!!!!
 
You raise a good point. Why can't they use citric acid with a twist of lemon in a car battery? No, they have to use sulphuric acid because they want to show they're tough or something.
Well, to seriously answer the question, I forget the scientific term but some molecules are very high on the positive potential, while others are very high on the negative. And I forget which each of these is which, but hydrogen and fluoride are the furthest apart on this measurement. So if you mix those two together (which is extremely difficult) they make the strongest acid that can even eat glass. Hydroflouric. Now the potential of a battery depends on the two metals involved and the strength of the acid (or alkali). Lead, copper and sulphuric acid make a pretty good, easy to make and therefore affordable battery.

Lemons and limes just aren't strong enough to make such a good battery. However, if you're squeezing them for juice, you'd better wear gloves. I made a key-lime pie without PPE and burned the cr@p out of my hands *once*. Learnt my lesson.....
 
But wouldn't it be cool if you could make a battery out of citric acid? Actually I seem to remember a science experiment where someone used a lemon to power something - Sorry, I tried to be more vague but struggled.

Sulphuric acid is nasty stuff. So is lead.

FWIW I squeeze a lot of citrus - lemons for cooking and limes for my wife's margaritas. Never had a problem. Except that these days arthritis makes it harder to do. I'm not old enough for arthritis! Oh, and apparently I cut my finger last week. Didn't notice until I squeezed a lime for a margarita then OUCH!
 
But wouldn't it be cool if you could make a battery out of citric acid? Actually I seem to remember a science experiment where someone used a lemon to power something - Sorry, I tried to be more vague but struggled.

Sulphuric acid is nasty stuff. So is lead.

FWIW I squeeze a lot of citrus - lemons for cooking and limes for my wife's margaritas. Never had a problem. Except that these days arthritis makes it harder to do. I'm not old enough for arthritis! Oh, and apparently I cut my finger last week. Didn't notice until I squeezed a lime for a margarita then OUCH!
Maybe it was just the key limes, they are very acidic. You don't cook the pie, the acid does. Sets up very nice and firm.....
 
I'm a PhD candidate in chemistry and love this kind of stuff, so at the risk of sounding like a massive pedant, an impromptu chemistry lesson...
Well, to seriously answer the question, I forget the scientific term but some molecules are very high on the positive potential, while others are very high on the negative. And I forget which each of these is which, but hydrogen and fluoride are the furthest apart on this measurement. So if you mix those two together (which is extremely difficult) they make the strongest acid that can even eat glass. Hydroflouric. Now the potential of a battery depends on the two metals involved and the strength of the acid (or alkali). Lead, copper and sulphuric acid make a pretty good, easy to make and therefore affordable battery.

Lemons and limes just aren't strong enough to make such a good battery. However, if you're squeezing them for juice, you'd better wear gloves. I made a key-lime pie without PPE and burned the cr@p out of my hands *once*. Learnt my lesson.....
You're sort of on the right track, but have a few terms confused here:
I forget the scientific term but some molecules are very high on the positive potential, while others are very high on the negative.
What you're describing here is electronegativity, which is the propensity of an atom to attract an electron. Fluorine (not fluoride, which already has an "extra" electron) is indeed the most electronegative element, but hydrogen and fluorine are not on opposite ends of this scale (fluorine has an electronegativity of ~4, hydrogen is 2.2 (values differ slightly depending on who you ask)). The least electronegative element (or most "electropositive" as we'd say) that we have reliable data for is cesium, the one that is the most diagonally opposed to fluorine in the periodic table. The redox reactions involving fluorine/fluoride and dihydrogen/H+ are also not on opposite ends of the scale, e.g. the alkali metals (especially lithium) are much more "negative" than dihydrogen/H+.
So if you mix those two together (which is extremely difficult)...
You're right that combining hydrogen gas and fluorine gas would be a terrible and super difficult way to make HF. Rather, the industrial route involves the decomposition of calcium fluoride with sulfuric acid, which is much easier (both those things are readily available bulk chemicals) (don't do this though, see below!!).
...they make the strongest acid that can even eat glass. Hydroflouric.
In chemistry the term "strong acid" means something specific. A "strong" (Brønsted) acid like hydrochloric acid will completely separate into H+ and X- (e.g. Cl-, or whatever the anion is) in water, whereas a "weak" acid will only partially separate (acetic acid, CH3COOH, the stuff in vinegar, is a quintessential weak acid - in water, there is some H+, CH3COO-, and leftover CH3COOH). Note that this has nothing at all to do with the "corrosiveness" of the acid. Hydrofluoric acid is actually a weak acid by this metric -- the reason it "eats glass" is due not to its acidity, but a different property of fluoride (F-). Glass is mostly silica (silicon dioxide, SiO2), and the silicon-fluorine bond is much stronger than the silicon-oxygen bond, so HF tears apart the Si-O bonds (i.e. destroys the glass) to make silicon fluorides and water. HF is also tremendously dangerous for a different reason: it readily permeates your skin and leaches the calcium from your bones, and other tissues. It is not something we take lightly.

But yes, the lead/sulfuric combination does indeed make a convenient and inexpensive high capacity battery, so it remains used to this day despite the hazards. Most hazards are manageable with appropriate controls!
 
Maybe it was just the key limes, they are very acidic. You don't cook the pie, the acid does. Sets up very nice and firm.....
I use lemons in a marinade for chicken. I cut chicken into small pieces and marinate in lemon juice, olive oil, salt, pepper and some herbs like thyme or oregano and then grill the chicken on a very hot griddle. It is absolutely delicious! The lemon tenderises the chicken and it doesn't take long. I like to eat it in wraps or toasted buns with lots of shredded lettuce, tomato and cucumber, some Thomy mayo and some chilli sauce. Nando's sauce is good. I cook this almost weekly and we never get tired of it.
 
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