Many questions about batteries.

[Stas]

Hi. I've been trying to get the concept of a battery in my head but I struggle to find info. Everything I've found so far is just very basic material.
I understand the positive cathode and negative anode. I'm a bit cloudy on electrolyte. Is it a liquid/paste solution that uses some medium like paper? If so, do the molecules of that medium participate in the charge/discharge process or is it simply for structure? Does the electrolyte exchange ions with either cathode or anode?
On to the next. After electrons travel from anode to cathode, how are the positive ions from anode able to cross to the cathode through electrolyte? Why can't electrons pass the same way?
How does application of energy reverse the process (recharging)?
What determines the cell's voltage?
Why does rechargeable battery "wear out?"
How and why does the memory effect occur?
Why are discharge rates different for different electrodes?
Why are there limits for max and min voltage in a Lithium cell?
How does permanent damage occur when the cell voltage is outside those limits?

I'm a bit overwhelmed with questions but would really like to learn this.
TIA

 

[silicon]

Well voltage in a battery is like water pressure in that it has a surplus of electrons or a potential that can flow, for example, thru a resister to create an electrical current. By allowing the current to flow the higher potential to the lower potential it has the effect of causing the battery to discharge its potential.
From wikipedia....
A zinc–carbon battery (or "heavy duty") is a battery packaged in a zinc can that serves as both a container and negative terminal. It was developed from the wet Leclanché cell (/lɛklɑːnˈʃeɪ/). The positive terminal is a carbon rod surrounded by a mixture of manganese dioxide and carbon powder. The electrolyte used is a paste of zinc chloride and ammonium chloride dissolved in water. Zinc chloride cells are an improved version from the original ammonium chloride variety. Zinc–carbon batteries are the least expensive primary batteries and thus a popular choice by manufacturers when devices are sold with batteries included. They are commonly labeled as general purpose batteries, while Zinc chloride cells are often labeled "Heavy Duty". They were the first commercial dry battery and made flashlights and other portable devices possible, because the battery can function in any position. They can be used in low drain or intermittent devices such as remote controls, flashlights, clocks or transistor radios. They are replaced, in many usages, by alkaline cells, and rechargeable NiMH batteries.

and a little more info here...
http://data.energizer.com/PDFs/carbonzinc_appman(dot)pdf

 

[piasabird]

When recharging batteries they can be damaged in different ways. Heat is one of them. Heat causes gassing If the battery is sealed, then it could expand and crack or catch on fire. Plus the gas is explosive and can blow up.

Also it is important that batteries can charge at different rates. So if you have a battery bank of say 20 6-volt batteries one bad battery can cause problems.

So what kind of batteries are you looking at?

What do you plan on using the batteries for?

I remind you that there were planes that were grounded because the Lithium batteries were catching fire.

 

[John Connor]

I understand the positive cathode and negative anode.

You have that backwards. It's positive anode and negative cathode.

 

[who?]

A diodes anode is positive a battery's anode is negative.

 

[John Connor]

Interesting. http://en.wikipedia.org/wiki/Anode

When I connect a DMM to a battery I must use the red probe otherwise it will show a negative number.

 

[serpretetsky]

Your first couple of questions on how batteries work need some chemistry. What you are looking for is called redox reactions. This is the basis of batteries. The rest is engineering to facilitate this redox process.

http://www.science.uwaterloo.ca/~cchieh/cact/c123/battery.html

 

[Paperdoc]

Let’s start with the basics of batteries. A Galvanic Cell (a single battery is composed of one or more such cells) consists of two DIFFERENT materials (usually metals) called the electrodes both immersed in a (normally liquid) solution called the electrolyte. The electrolyte has dissolved in it chemicals related to the two electrodes, and these are dissociated into ions. The ions can move around in the electrolyte, and thus can carry a current from one electrode to another. In many sealed batteries the electrolyte also has added to it something to make it semi-solid or paste-like so that it won’t flow easily mechanically and leak, even though the ions in it can still move quickly. In some designs there is also some inert matrix material (like a glass fibre mat) soaked with the electrolyte and holding it in place to keep it from moving. The battery stores energy as a mixture of CHEMICALS that can change during use or recharging – it does not store energy as electrical charges.

Each electrode has an external connector or terminal. When the battery is first assembled the components reach an equilibrium condition in which the two electrodes are at different electrical potentials, so there is a voltage across the battery terminals. As long as nothing is attached to those terminals to allow current to flow, nothing changes and the battery remains “charged”. (Well, actually, it will slowly degrade and lose change (voltage decreases) due to minor side reactions, but ideally this is a very slow process.)

Things change when a current path (an electrical load) is attached to the terminals. At the CATHODE, metal atoms release one or more electrons (chemists call this oxidation of the metal) each, producing positive ions of that metal that dissolve and leave into the electrolyte solution. This leaves behind excess electrons that can flow out of the Cathode terminal and through the external load to the other terminal. Meanwhile, at the surface of the ANODE, ions of its metal approaching from the electrolyte accept electrons from the Anode to convert them into metal that deposits on the Anode (Chemists call this reduction). To the external circuit, electrons are flowing through it and electrical energy is being used. Inside the battery cell, two types of chemical reactions are occurring – oxidation and reduction. The net result is that metal from the Cathode is being converted into ions of that metal and released into the electrolyte, while ions of the Anode’s metal are being removed from the electrolyte and deposited as metal onto the Anode. This alters the original balance of concentrations of the two metal ions in the electrolyte solution. The result is that the battery voltage slowly decreases until it gets too low to serve the needs of the external load.

In theory, the two chemical reactions involved can be reversed. If you use an external source of electrical power and apply to the terminals of the battery a voltage that is opposite in direction to the battery’s normal voltage and slightly larger, you can force current to run backwards through the battery. This means that each of the two chemical reactions at the electrode terminals are forced to go in reverse, thus pushing the balance of metal ions in the electrolyte solution back to its original starting point. This is how you recharge the battery. In some types of cells this is not practical to do because of excess heat or production of gases, and that type of battery is called “disposable”. For example, trying to recharge a common Carbon-Zinc sealed flashlight battery will cause it to crack open the zinc outer can and leak electrolyte paste, so it should never be done. But there are many battery types that CAN be recharged in this manner. Common examples are automobile Lead acid batteries and Nickel- Cadmium or Nickel-Metal Hydride batteries in electronic devices.

There are two vitally important issues in recharging batteries designed for that use. The first is the actual voltage. The charging circuit must supply a higher voltage than the current battery voltage in order to force a current to flow through. However, once the battery is returned to its fully-charged design state, the charging circuit must NOT supply a higher voltage and try to keep overcharging. Now, every battery design has a specific voltage at full charge, so the battery charger used must be designed for that battery type to make sure its voltage is set correctly. Secondly, some battery types can be charged more efficiently, and with less risk of internal damage, if the charging current is carefully regulated. In fact, some systems require different current at different stages of recharging. So again, a good charger is customized for the specific battery it is intended for.

In electrochemistry there is a famous mathematical model, called the Nernst Equation, which relates the Free Energy of the chemical reactions involved in a particular cell, the concentrations of its components, the battery temperature, and the voltage you get as a result at the battery terminals. For practical purposes, it shows two important characteristics of all batteries. One is that as component concentrations change the output voltage changes, as discussed above. The other is that output voltage will decrease as battery temperature drops. Ask any hardy northerner about the problems trying to start a car at 35 below!

 

[Zeldak]

Let’s start with the basics of batteries. A Galvanic Cell (a single battery is composed of one or more such cells) consists of two DIFFERENT materials (usually metals) called the electrodes both immersed in a (normally liquid) solution called the electrolyte. The electrolyte has dissolved in it chemicals related to the two electrodes, and these are dissociated into ions. The ions can move around in the electrolyte, and thus can carry a current from one electrode to another. In many sealed batteries the electrolyte also has added to it something to make it semi-solid or paste-like so that it won’t flow easily mechanically and leak, even though the ions in it can still move quickly. In some designs there is also some inert matrix material (like a glass fibre mat) soaked with the electrolyte and holding it in place to keep it from moving. The battery stores energy as a mixture of CHEMICALS that can change during use or recharging – it does not store energy as electrical charges.

Each electrode has an external connector or terminal. When the battery is first assembled the components reach an equilibrium condition in which the two electrodes are at different electrical potentials, so there is a voltage across the battery terminals. As long as nothing is attached to those terminals to allow current to flow, nothing changes and the battery remains “charged”. (Well, actually, it will slowly degrade and lose change (voltage decreases) due to minor side reactions, but ideally this is a very slow process.)

Things change when a current path (an electrical load) is attached to the terminals. At the CATHODE, metal atoms release one or more electrons (chemists call this oxidation of the metal) each, producing positive ions of that metal that dissolve and leave into the electrolyte solution. This leaves behind excess electrons that can flow out of the Cathode terminal and through the external load to the other terminal. Meanwhile, at the surface of the ANODE, ions of its metal approaching from the electrolyte accept electrons from the Anode to convert them into metal that deposits on the Anode (Chemists call this reduction). To the external circuit, electrons are flowing through it and electrical energy is being used. Inside the battery cell, two types of chemical reactions are occurring – oxidation and reduction. The net result is that metal from the Cathode is being converted into ions of that metal and released into the electrolyte, while ions of the Anode’s metal are being removed from the electrolyte and deposited as metal onto the Anode. This alters the original balance of concentrations of the two metal ions in the electrolyte solution. The result is that the battery voltage slowly decreases until it gets too low to serve the needs of the external load.

In theory, the two chemical reactions involved can be reversed. If you use an external source of electrical power and apply to the terminals of the battery a voltage that is opposite in direction to the battery’s normal voltage and slightly larger, you can force current to run backwards through the battery. This means that each of the two chemical reactions at the electrode terminals are forced to go in reverse, thus pushing the balance of metal ions in the electrolyte solution back to its original starting point. This is how you recharge the battery. In some types of cells this is not practical to do because of excess heat or production of gases, and that type of battery is called “disposable”. For example, trying to recharge a common Carbon-Zinc sealed flashlight battery will cause it to crack open the zinc outer can and leak electrolyte paste, so it should never be done. But there are many battery types that CAN be recharged in this manner. Common examples are automobile Lead acid batteries and Nickel- Cadmium or Nickel-Metal Hydride batteries in electronic devices.

There are two vitally important issues in recharging batteries designed for that use. The first is the actual voltage. The charging circuit must supply a higher voltage than the current battery voltage in order to force a current to flow through. However, once the battery is returned to its fully-charged design state, the charging circuit must NOT supply a higher voltage and try to keep overcharging. Now, every battery design has a specific voltage at full charge, so the battery charger used must be designed for that battery type to make sure its voltage is set correctly. Secondly, some battery types can be charged more efficiently, and with less risk of internal damage, if the charging current is carefully regulated. In fact, some systems require different current at different stages of recharging. So again, a good charger is customized for the specific battery it is intended for.

In electrochemistry there is a famous mathematical model, called the Nernst Equation, which relates the Free Energy of the chemical reactions involved in a particular cell, the concentrations of its components, the battery temperature, and the voltage you get as a result at the battery terminals. For practical purposes, it shows two important characteristics of all batteries. One is that as component concentrations change the output voltage changes, as discussed above. The other is that output voltage will decrease as battery temperature drops. Ask any hardy northerner about the problems trying to start a car at 35 below!

+1! Very nice Paperdoc!

 

[Zeldak]

I don't know the chemistry of "memory effect." The battery's voltage is determined by the chemicals involved. "Hotter" components make higher voltages. Most common batteries are 1.5 volts. There is more "chemical stuff" in the bigger ones, so they can maintain the same voltage output longer or give "more" current at their intrinsic voltage (D batteries vs. AAA). Shelf life is determined by how well the internal components are effectively isolated from each other in the absence of a circuit. Over time, whether sitting around or being used, the internal chemicals achieve equilibrium--which means the battery is dead. Rechargeable batteries are made to facilitate the reversal of the chemical reactions that generate the voltage. When THEY reach equilibrium, they won't do anything anymore, and they are dead. Any heat your battery generates in the process of generating current is wasted energy. NiCad rechargeable batteries like to be stored "empty" of charge. Lithium batteries like to be stored "full." Lithium batteries are obviously less sensitive to memory effect, which is the point of ignorance where I began. Submarines use a LOT of batteries. Nuclear subs can continue to recharge their batteries while submerged, diesels can't.

 

[Colt45]

Lithium actually likes to be stored at 40% charge, something like that. (for long term). Full charge is ok, but it will lose more capacity.

 

[Stas]

Things change when a current path (an electrical load) is attached to the terminals. At the CATHODE, metal atoms release one or more electrons (chemists call this oxidation of the metal) each, producing positive ions of that metal that dissolve and leave into the electrolyte solution. This leaves behind excess electrons that can flow out of the Cathode terminal and through the external load to the other terminal. Meanwhile, at the surface of the ANODE, ions of its metal approaching from the electrolyte accept electrons from the Anode to convert them into metal that deposits on the Anode (Chemists call this reduction). To the external circuit, electrons are flowing through it and electrical energy is being used. Inside the battery cell, two types of chemical reactions are occurring – oxidation and reduction. The net result is that metal from the Cathode is being converted into ions of that metal and released into the electrolyte, while ions of the Anode’s metal are being removed from the electrolyte and deposited as metal onto the Anode. This alters the original balance of concentrations of the two metal ions in the electrolyte solution. The result is that the battery voltage slowly decreases until it gets too low to serve the needs of the external load.

Ah, this was a crucial piece of information. The ions are actually IN the electrolyte. Many diagrams I saw showed the ions travel from Cathode through electrolyte TO Anode. That made no sense to me, as it looked like both metals were swapping locations.

There are two vitally important issues in recharging batteries designed for that use. The first is the actual voltage. The charging circuit must supply a higher voltage than the current battery voltage in order to force a current to flow through. However, once the battery is returned to its fully-charged design state, the charging circuit must NOT supply a higher voltage and try to keep overcharging. Now, every battery design has a specific voltage at full charge, so the battery charger used must be designed for that battery type to make sure its voltage is set correctly. Secondly, some battery types can be charged more efficiently, and with less risk of internal damage, if the charging current is carefully regulated. In fact, some systems require different current at different stages of recharging. So again, a good charger is customized for the specific battery it is intended for.

What happens, chemically, when you overcharge the battery then?

Lithium actually likes to be stored at 40% charge, something like that. (for long term). Full charge is ok, but it will lose more capacity.

Yup, this I know.

 

[Stas]

Looked over this: http://en.wikipedia.org/wiki/Nernst_equation
Too complex for me to figure out right now. I want to understand what the cell's potential is determined by. At least the major contributor, if there are several. Is it the number of electrons in participating metal atoms? The strength of attraction in the same atoms? Proportions of cathode and anode? Something else?

 

[Paperdoc]

Near the top of the Wikipedia article under the heading "Expression" are two equations. The first is for one half of a battery - a "half cell". In electrochemistry, every element can be set up in a half cell with the other half as a standard "reference electrode". This latter reference point is defined to have zero Reduction Potential. So any test cell set up with this reference electrode will have a voltage equal to the Reduction Potential of the half cell of the test material. The measurement is done under certain constant defined conditions of temperature, concentration, etc. There are tables of Standard Reduction Potentials available based on these measurements. Those are the E(0) values in the equation. (Sorry I can't write that with the superscript theta character that Wikipedia used.) The first equation in the article is that for such a half cell.

If we now create a battery (well, one cell, not many in series) from two different materials and using the "standard" concentrations in the electrolyte solution, the cell voltage will just be the difference between the two half cells. The second equation in the article covers this total cell.

Now for the rest of the factors in the Nernst Equation. R is just the Universal Gas Constant that crops up everywhere in Chemistry. T is the absolute temperature in Kelvin. The conversion from Celsius temperature is simple: T (K) = t (C) + 273.15. z is simply the number of electrons changed for each metal atom that is converted to an ion, or converted the other way. F is a special constant, the Faraday Constant, defining the relationship between one mole of a chemical and one Coulomb of electrical charge. The "a" values are a product of actual concentration of one of the ions in the electrolyte times an activity coefficient. In dilute solutions, most ions behave ideally, but in more concentrated solutions they may behave as is they were at reduced concentration because not all of them are free and active, so using "a" instead of simply the "C" or concentration takes this into account. Also note that this means we have some ability to manipulate the voltage of a cell beyond just selecting its materials - we can also decide to use non-standard concentrations of ions in the electrolyte solution.

In terms of practical things one can manipulate, the most significant terms are the materials chosen for each half of the full cell (those determine the two half-cell Standard Reduction Potentials), the concentrations of the ions in the electrolyte (which change as the battery is used or recharged), and the (absolute) temperature of the battery.

As a completely side issue but very much related, the Nernst Equation also explains one mechanism for corrosion of metals in the presence of salts and water - for example, the way car bodies in winter are attacked by road salt. Those conditions create what are known as Concentration Cells. In these we have two nearby areas that are both part of the car's metallic body, so there is an electrical conduction path between them. We also have both water and salt present. BUT the trouble is that the concentration of salt is DIFFERENT at two different spots on the car body. So the Nernst Equation shows us that this means there are two DIFFERENT half-cell potentials at those points (different solely because of ion concentrations, even though the metal is the SAME at those two points) and we have a full cell with an external conduction path. So guess what: at the place where there is more salt concentration, the metal is oxidized into ions that wash away, leaving holes in the metal!

All of that stuff is about the VOLTAGE of a battery under near-zero load. The CURRENT you can get flowing from a battery through the external load depends on a whole bunch of other factors like the size of the internal components, their electrical resistance, the surface condition of the electrodes inside, etc.

 

[Stas]

Awesome info, sir. Thank you very much. Tell me, if my reasoning is correct while applying that info. Sanyo makes a NiMH battery with this chemistry
http://www.eneloop.info/uploads/pics/Technology_icon2.jpg

Based on this table - http://www.av8n.com/physics/redpot.htm, NiOOH is about 0.5V. Mn is something around ~1.5V and Co is ~1.8V. The concentrations in the anode are unknown, so assume 50/50. (1.5+1.8)/2=1.65. 1.65-0.5=1.15V. Close enough to the nominal voltage of the actual Eneloop cell, which is 1.2V. Am I doing this right?
http://www.eneloop.info/eneloop-products/eneloop-batteries/eneloop.html

 

[Paperdoc]

You have the right idea, but the details need a touch-up. In that table of SRP's, you need to search for the specific reactions used in the cells. The eneloop drawing is not very specific, but one half cell involves a reaction of NiOOH producing OH- as an electron is consumed. This reaction is in the table just below the middle, and its SRP is +0.49v. The other half-cell involves some reaction of Co and Mn producing precipitated (solid) metal. In the table, the one for Co(OH)2 (solid) consuming 2 electrons to produce Co metal (solid) is ¼ way down from the top, with a SRP of -0.73v. Somewhat above that is the similar reaction for Mn(OH)2 with a SRP of -1.55v. Now I don't know exactly what reaction system the battery is is using, but if you ignore the Mn and look at the Ni and Co half cells and subtract them (you have to subtract, since all of the standard cell reactions are written as if they CONSUME electrons, but there has to be a balance of generation and consumption in a full cell), the E(0) for the cell is +0.49 - (-0.73) v = 1.22v. That's close to the nominal for the eneloop cells.

 

[Dude111]

My Poser is about Rechargable batterys!

Is it possible to TOTALLY DRAIN IT TO 0VOLTS and recharge it?? (I have one that doesnt hold the charge for long and I would love resetting it and then trying to charge it full!! (If its possible))

ONE REASON I HATE THESE KINDS OF BATTERIES!!

 

[JManInPhoenix]

Lot of good info here, especially from Paperdoc.

For someone that wants a really basic (written at about the middle school level) explanation of basic electricity, ac/dc, batteries, etc, the old navy NEETS manuals are pretty decent. You can get a PDF copy here: http://www.hnsa.org/doc/neets/mod01.pdf

 

[Dude111]

Gracious,i will take a gander at it!

 

[Stas]

You have the right idea, but the details need a touch-up. In that table of SRP's, you need to search for the specific reactions used in the cells. The eneloop drawing is not very specific, but one half cell involves a reaction of NiOOH producing OH- as an electron is consumed. This reaction is in the table just below the middle, and its SRP is +0.49v. The other half-cell involves some reaction of Co and Mn producing precipitated (solid) metal. In the table, the one for Co(OH)2 (solid) consuming 2 electrons to produce Co metal (solid) is ¼ way down from the top, with a SRP of -0.73v. Somewhat above that is the similar reaction for Mn(OH)2 with a SRP of -1.55v. Now I don't know exactly what reaction system the battery is is using, but if you ignore the Mn and look at the Ni and Co half cells and subtract them (you have to subtract, since all of the standard cell reactions are written as if they CONSUME electrons, but there has to be a balance of generation and consumption in a full cell), the E(0) for the cell is +0.49 - (-0.73) v = 1.22v. That's close to the nominal for the eneloop cells.

Thank you, Paperdoc. Can you explain the current capacity in a cell? I'm assuming different compounds would yield different density. What chemical properties affect the phenomenon?

 

[Paperdoc]

Actually, no, I can't. I trained as a Physical Chemist and that certainly included Redox reactions and electrochemistry, but I've never worked in the field of batteries, nor have I ever looked closely at the details of battery construction. I expect that the physical size (and hence surface area) of the electrodes and the concentrations of the ions in the electrolyte solution have impacts on current flow. I'm also quite sure there are many other factors like inert materials in the electrolyte to alter its physical characteristics (e.g. paste electrolytes, gel cells, fibreglass support mats), trace components of the electrolyte solution, etc. are important factors. These sorts of things manifest themselves in part as the "Internal Resistance" of the battery. What? Every real battery can be modelled as two "ideal" components inside the case: an ideal battery that provides a voltage independent of current, and in series with it an ideal resistance that reduces the terminal voltage according to the current being drawn. You might also include a third "ideal" component inside the battery - a high resistance in parallel with the rest of it that accounts for the slow discharge of a battery in storage. It is that Internal Resistance that makes the terminal voltage go down as the battery output current it raised.

As a practical example of the impact these factors have, here are some observations on automobile batteries - I've worked often with these as a "backyard mechanic".
Good new battery in the summer, no load connected: 13.2 volts at the terminals

Good new battery in the summer, key turned and the starter motor running to start the engine: 10 to 11 volts at the terminals, probably about 100 to 120 amps current being drawn

Good new battery in the summer, engine running at idle after the car has been started: 14.5 volts at the terminals (slightly higher than original battery voltage because the charging circuit is forcing current back into the battery)

Good new battery in the winter (35 below F), no load connected: 12.0 volts at the terminals (a little lower than summer from temperature effect on E(0))

Good new battery in the winter (35 below F), key turned and the starter motor running to start the cold, stiff engine: 8 to 10 volts at the terminals, probably about 130 to 160 amps current being drawn (note higher current for stiff engine)

Old worn-out battery in the winter (35 below F), no load connected: 11.2 volts at the terminals (looks OK, right?)

Old worn-out battery in the winter (35 below F), key turned and the starter motor running to start the cold, stiff engine: less than 6 volts at the terminals, probably about 50 amps current being drawn, often less because the battery voltage has dropped so low it can't push a heavy current through the starter circuit. This is when the starter motor turns too slowly to start the engine, or more commonly, does not turn at all. The root problem is two-fold: the ion concentrations in the electrolyte solution have altered substantially because the battery is not fully charged, AND the factors that determine the Internal Resistance have degraded so much inside the battery that its resistance is MUCH higher than "normal", and the battery simply cannot keep terminal voltage up when a current is flowing out. Car does not start!

 

[serpretetsky]

My Poser is about Rechargable batterys!

Is it possible to TOTALLY DRAIN IT TO 0VOLTS and recharge it?? (I have one that doesnt hold the charge for long and I would love resetting it and then trying to charge it full!! (If its possible))

ONE REASON I HATE THESE KINDS OF BATTERIES!!

Most batteries i know of, including lithium ion and nimh, do not like being discharged to 0 volts. It can be destructive. Batteries typically have a certain voltage they provide, even when near completely discharged.

Many people recommend discharging nimh when you store them, however, that is usually about 0.8V/ cell, not zero. Most people do not recommend discharging lithium ion batteries AT ALL, unless you want to reset the internal energy remaining estimation circuitry (which has nothing to do with the battery chemistry and therefore actual battery life). So I wouldn't recommend it.

No battery tactics help your battery get more "life" than they had before. They just slow down the natural aging of your battery.

If you have a battery that doesn't hold charge for very long, there usually isn't much you can do. Time to get a new battery.

edit: this may not apply to non-sealed lead acid batteries (the kind that you add sulphuric acid to). I'm not familiar with these.

 

[natto fire]

Most batteries i know of, including lithium ion and nimh, do not like being discharged to 0 volts. It can be destructive. Batteries typically have a certain voltage they provide, even when near completely discharged.

Many people recommend discharging nimh when you store them, however, that is usually about 0.8V/ cell, not zero. Most people do not recommend discharging lithium ion batteries AT ALL, unless you want to reset the internal energy remaining estimation circuitry (which has nothing to do with the battery chemistry and therefore actual battery life). So I wouldn't recommend it.

No battery tactics help your battery get more "life" than they had before. They just slow down the natural aging of your battery.

If you have a battery that doesn't hold charge for very long, there usually isn't much you can do. Time to get a new battery.

edit: this may not apply to non-sealed lead acid batteries (the kind that you add sulphuric acid to). I'm not familiar with these.

I'm glad you posted this, as I have a question about the ideal storage charge of Li-ion batteries. In my research, it seems like 20-40% SoC is ideal for long term storage, but I was wondering if this was only for a certain type of Lithium chemistry.

I am interested in the iron phosphate derivative, as I have lots of cordless tool batteries that can sit for weeks-months without being attended to. The batteries have a built in gauge which shows the approximate charge through 4 LEDs. When I got the batteries (a total of 7 purchased at various times throughout the past couple years) the indicators were always showing 2 "bars" worth of charge, and I assumed that was the ideal SoC for the warehousing or distribution of them.

I have been sticking to this strategy, and over 2 years after ever buying one of these batteries have yet to have one show any significant storage loss. It's tricky to test exactly, as the tools use a wildly varying amount of power to do the work at hand.

Just wondering if this 20-40% thing mainly applies to lithium polymer, and I am wasting my time making sure all of my LiFePO batteries are at a certain charge before storing them.

 

[serpretetsky]

I'm glad you posted this, as I have a question about the ideal storage charge of Li-ion batteries.

...
...

Just wondering if this 20-40% thing mainly applies to lithium polymer, and I am wasting my time making sure all of my LiFePO batteries are at a certain charge before storing them.

My knowledge on batteries is not of a very technical nature. Everything I know is from general internet research. I don't really know the details and do not understand the chemical reasoning for most of it.

So I really don't know. Like you, I generally try to keep my Lion batteries around 50% charged for storage (i usually go 50% to give them a little room to slowly drain when you store them). I'm not familiar with LiFePO batteries.