Electronics, Lighting, & Gadgets - How to charge a single AA battery?

My cheap 2-hour walmart charger can only work if 2 or 4 batteries are inside it. If I put just one in, it won't work. Can I charge a dead one with a fully charged one? Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

Buy a decent charger and stop frying your batteries.

What is a decent charger you recommend?

Nimh or nicad ?

It's tricky, I'm not in the same country as you.

However some cheap chargers trickle charge 4 batteries in parallel but independently - because they trickle charge you can estimate charge time based on capacity and overcharging isn't an issue because the current is so low.

I use a computerised charger.

I strongly suspect that your 2 hour charger just outputs high current for 2 hours and then stops - not very good for a partly discharged or lower capacity battery.

Hope this helps....

:)

I have a LaCrosse and it's worked fine for me. It came with a nice set of batteries to get started with.

http://www.lacrossetechnology.com/900/index.php

This is my charger ( nimh ):

http://i.walmartimages.com/i/p/00/02/13/31/25/0002133125859_500X500.jpg

I think it has some intelligence not to overcharge since it automatically turns off when batteries are charged.

That's a 1 hour charger ?

That's a 1 hour charger ?

I couldnt find my exact model, but that is quite close to mine.

See

Battery Charger Comparison (http://greenbatteries.com/batterychargercompare.html)

From the chargers listed there, I have TurboCharger 4000 and am very pleased. It has a thermal switch that terminates the charging if the batteries begin to heat up. There are other smart charger options there, including the possibility to charge an odd number of cells. Simple chargers either take forever to charge or fry the batteries. I would not charge a set where one battery is dead - either the other will not charge or you will have a good chance to damage the other as well.

If you are lucky the charger is cutting off before the battery has reached full capacity as it isn't possible to properly charge a NIMH that quickly.

In any case the number of charges you get from the batteries will be a lot less than careful charging and the capacity will drop a lot quicker too.

It's a trade off - you get the convenience of a fast charge - the batteries pay the price.

Higher capacity batteries are not suitable for fast charging.

:)

generally any charger will work in this situation.

you don't need a fancy charger, despite what others may claim.

better off buying a cheap multimeter so that you can make this determination yourself.

typically they'll all (2 or 4 cells) charge to within 0.1v of endpoint

generally any charger will work in this situation.

you don't need a fancy charger, despite what others may claim.

Oh really ?

Just how does a 2 hour charger detect the negative delta V of each battery when it has a minimum of two batteries attached to it ?

And isn't capable of charging individual batteries ?

Sigh....

you don't need a fancy charger, despite what others may claim.

better off buying a cheap multimeter so that you can make this determination yourself.

typically they'll all (2 or 4 cells) charge to within 0.1v of endpoint

0.1V of what endpoint?? The consumer is supposed to take measurements with a meter, produce a chart and decide that the voltage has already gone through the peak, very weakly pronounced in the case of NiMH. I would appreciate if you could record your actions and post them on YouTube or elsewhere so all of us stupid getting smart chargers could learn.

0.1V of what endpoint?? The consumer is supposed to take measurements with a meter, produce a chart and decide that the voltage has already gone through the peak, very weakly pronounced in the case of NiMH. I would appreciate if you could record your actions and post them on YouTube or elsewhere so all of us stupid getting smart chargers could learn.

+1 if you are using a cheap charger you are either going to over or undercharge every battery you put in it - what are you suggesting, checking the battery with a multimeter every 10 seconds in a vain hope of detecting a minute voltage drop ??

I think the OP is hoping for good advice. :(

Would just like to say that I don't like FAST chargers.

A big problem with the 1/2hour chargers is that the battery gets very warm, and the heat drastically shortens its lifetime re charging cycles, but does, in my experience seem to effect the length of each actual charge as well.

I find 6-8 (12 if necessary) hours depending on capacity adequate.

Lets face it, if you need a battery NOW, it would make little difference if it was an hour away or 12 hours away, you still wouldn't have it NOW.

Lower-priced chargers may not apply a fully saturated charge. Some will indicate full-charge immediately after a voltage or temperature peak is reached. These chargers are commonly sold on the merit of short charge time and moderate price.


A well-designed charger is a reasonably complex device. Taking short cuts will cost the user in the long run. Choosing a well-engineered charger will return the investment in longer lasting and better performing batteries.

:)

A billion people recharge batteries successfully every day, simply by following the instructions - all without the sage wisdom expressed in this thread.

A billion people recharge batteries successfully every day, simply by following the instructions - all without the sage wisdom expressed in this thread.

The OP asked for advice - take it up with him.

better off buying a cheap multimeter so that you can make this determination yourself.

typically they'll all (2 or 4 cells) charge to within 0.1v of endpoint


A billion people recharge batteries successfully every day, simply by following the instructions - all without the sage wisdom expressed in this thread.

Oops, I thought you were the source for the wisdom.

A billion people recharge batteries successfully every day, simply by following the instructions - all without the sage wisdom expressed in this thread.

But how many actually realise the full life time form their batteries?

I can tell you that before I became wise to the pitfalls of cheap and/or fast chargers, I was having under 1 year old and under 100 charge cycle batteries going flat far too quickly or just not holding a charge at all, constantly.

1 decent charger later and I have not had a single battery to date that has not met its expectations.

I am a big fan of the new hybrid batteries too.


Anyway, advice was asked for, and has been given.

Whether it is good advice or not, that is for the OP to decide.

A billion people recharge batteries successfully every day, simply by following the instructions - all without the sage wisdom expressed in this thread.

And while we are talking of sage wisdom:


generally any charger will work in this situation.
you don't need a fancy charger, despite what others may claim.
better off buying a cheap multimeter so that you can make this determination yourself.
typically they'll all (2 or 4 cells) charge to within 0.1v of endpoint

Ha ha ha ha ha ha ha ha !!!!

:roflmao2: :roflmao2: :roflmao2: :roflmao2: :roflmao2: :roflmao2: :roflmao2: :roflmao2: :roflmao2: :roflmao2:

Thanks for all the replies, I take it the answer to my question below is no.

Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

Thanks for all the replies, I take it the answer to my question below is no.

Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

Your cheapo wal-mart charger... - Probably not.

There are chargers that will charge individual batteries - and even tell you if a cell is dead.

You pays ya money and takes ya choice.

Thanks for all the replies, I take it the answer to my question below is no.

Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

I'll try to answer accurately: No, I dont believe it is possible.


A nickel-metal-hydride charger must respond to a voltage drop of 8-16mV per cell. Making the charger too sensitive may terminate the fast charge halfway through the charge due to voltage fluctuations and electrical noise. Most of today's nickel-metal-hydride chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge.

Note: that refers to intelligent chargers

There are several ways a charger can detect when a battery is fully charged and a decent charger will often use several at the same time.

If your charger has a temperature monitor it might cut off before the healthy battery is too badly damaged.

If your charger detects the delta peak (very unlikely when charging 2 batteries in parallel) I would say you have no chance of not damaging the healthy battery.

Sorry, a cheap charger is a cheap charger.

Thanks for all the replies, I take it the answer to my question below is no.

Is the charger smart enough to know to only charge the dead one and not overcharge the already charged one?

A charger that charges cells in pairs, takes the pair connected in series. A smart charger will usually figure out that something is wrong and refuse to charge or will switch to a trickle mode. It has no means of disconnecting those cells from each other. The dumbest fast chargers have only a time cut-off and will try to proceed with an unclear outcome.

You pays ya money and takes ya choice.

See post #5. Using it right now doing a nice slow 200 mA charge. With 2 AA's in that baby it will do 1800 mA.

I have a 1hr energizer charger that will do 1-2-3 or 4 cells, AA or NiMh. Its cheap and the batteries end up too hot to hold. When I was running 12AA battery packs I used it for a while.. Lots of dead cells now.
I no longer use this charger, figuring cells aren't really that cheap.

cells aren't really that cheap.

A little over a buck a piece for some generic. That's not too bad.

compared with their generic alkaline counterparts?

If you are going to fry Rechargeables you might as well spend out on alks or even lithium, as in the long run it will cost the same.

HOWEVER - invest in a decent charger and soon the rechargeable starts paying for iteslf

compared with their generic alkaline counterparts?

If you are going to fry Rechargeables you might as well spend out on alks or even lithium, as in the long run it will cost the same.

HOWEVER - invest in a decent charger and soon the rechargeable starts paying for iteslf

I'm not sure I understand your point. Here's what I'm saying. For a little over a buck, I can get a rechargeable nimh that can be used many times over even if I don't take care of it and fry the hell out of it. Much more cost efficient than an alkaline.

We're saying the same thing, right?

maybe - the cheapes (US$) I have seen lithiums for is ~0.75c. Why go to through the hassle of charging if ya gonna fry?

With the lithiums you are guaranteed to have pretty much good cells.

If you are frying - you have no idea how good the cells are and how long they will last. PLUS you have had to charge them (however long that takes). Plus you have spent the electricity to charge them (marginal I know) AND you have had to buy the charger to fry them with.

I If you are going to use rechargeables, then it is worthwhile investing in a decent charger. It doesn't have to charge one at a time, but it does need to be "smart"

Rather than invest in a new charger, is there a simple way I can drain my AA battery so I can charge it properly with my dead one? Can I short circuit it?

I If you are going to use rechargeables, then it is worthwhile investing in a decent charger. It doesn't have to charge one at a time, but it does need to be "smart"

We agree. :thumb:

Rather than invest in a new charger, is there a simple way I can drain my AA battery so I can charge it properly with my dead one? Can I short circuit it?

The Cold Heat soldering iron relies on short-circuiting AA batteries across the soldered elements. With the steps you propose you might be on the way to force yourself to invest in (a) new batteries, (b) new charger and (c) maybe even new home, if you leave badly damaged batteries in a dumb fast charger.

Seriously, DO NOT try it. Buy extra batteries. After a while, another one will die.

Buy an inexpensive adjustable current-regulated power supply. Charge at C/10 or less. When the battery starts to feel warm then it is fully charged.

I have the C204F. http://www.users.on.net/~mhains/Table2.html

Buy an inexpensive adjustable current-regulated power supply. Charge at C/10 or less. When the battery starts to feel warm then it is fully charged.

I believe this to be very bad advice because:

1) If the battery starts to feel warm at C/10 it could already very overcharged (if the battery is partially charged to start with) by the time you check or depending on capacity/internal resistance the battery could get warm 1/2 way through the charging process.

We aren't baking a cake here, you know.

2) Nimh have much poorer overcharge absorption than Nicad and will be damaged if trickle charged at more than 0.05C. The Nimh simply can't absorb the extra power after they reach peak saturation.

3) Slow charges cause crystalline formation (memory).

While these are all bad things - Nimh do not like being trickle charged - I believe cheap fast chargers are more damaging.

If you don't mind having batteries that are always overcharged or undercharged and have greatly shortened life expectancy (hundreds of cycles less), use a cheap charger.

:)

Charging NiMH at C/10 or under is commonly done with good results. I personally do this and have some NiMH battery packs that are 8 years old and still cycle to near capacity.

In my experience a limited overcharge at this rate is not a problem, but they should not be left on charge permanently. One can either charge for a set amount of time (say 14 hours at C/10) and accept that there will be some overcharge or terminate the charge when a small rise in temperature is noticed. The temperature rise is perceptible when charging AA cells at 150 mA or higher. I'm not sure it will be noticeable at lower charge rates. It is probably best to use both criteria, i.e., if no temp rise is felt after 14 hours then stop the charge.

I believe (this is just an opinion) that memory effect is nonexistent in NiMH cells. There is no need to cycle NiMH cells other than to check their capacity.

If you are charging at C/10 and can feel a temperature increase at the end of the charge cycle that doesn't mean it is fully charged, it means it is failing to absorb the overcharge and you aren't doing the battery any favours.

+1 for any Maha

NiMH DO suffer from memory effect (or what people think is memory effect anyway), just not as much as NiCd.

Some useful info here (http://www.buchmann.ca/Article10-Page1.asp) and here (http://www.dansdata.com/gz011.htm)

+1 for any Maha

Are they the constant current pulse chargers?

I was looking at them today

Are they the constant current pulse chargers?

I was looking at them today

They call their tech FLEX negative pulse charging though I don't know what that means or whether their "conditioning" claims are true. I can tell you that in practice I have owned a C401 series for years now and have yet to throw away a battery purchased since. It even made some of the batts fried by a cheap Rayovac useable again, though limited in capacity. It has been worth every penny.

http://en.wikipedia.org/wiki/Battery_charger

Pulse

Some chargers use pulse technology in which a pulse is fed to the battery. This DC pulse has a strictly controlled rise time, pulse width, pulse repetition rate (frequency) and amplitude. This technology is said to work with any size, voltage, capacity or chemistry of batteries, including automotive and valve-regulated batteries.[2][3] With pulse charging, high instantaneous voltages can be applied without overheating the battery. In a Lead-acid battery, this breaks-down stubborn lead-sulfate crystals, thus greatly extending the battery service life.[4]

Several kinds of pulse charging are patented.[5][6][7] Others are open source hardware.[8]

Some chargers use pulses to check the current battery state when the charger is first connected, then use constant current charging during fast charging, then use pulse charging as a kind of trickle charging to maintain the charge.[9]

Some chargers use "negative pulse charging", also called "reflex charging" or "burp charging".[10] Such chargers use both positive and brief negative current pulses. Such chargers don't work any better than pulse chargers that only use positive pulses.[11][12]


RE: negative pulse charging
http://www.rcbatteryclinic.com/burp.html



And some good advice on fast charging
http://www.rcbatteryclinic.com/ (http://www.rcbatteryclinic.com/fastchrg.html)

Most 'pulse' chargers are just using semi-rectified A/C. :)

If you are charging at C/10 and can feel a temperature increase at the end of the charge cycle that doesn't mean it is fully charged, it means it is failing to absorb the overcharge and you aren't doing the battery any favours.

Unknown, I don't understand the distinction you are making. When a cell is fully charged it will dissipate any further charge energy as heat. This is an indication that the cell is fully charged. At low charge rates the heat is not damaging to the cell. This is why Sanyo and other manufacturer's state a standard timed charge rate at C/10.

On the other hand, cells can be damaged by use of an unreliable peak-detect charger. Because peak detect chargers charge at a relatively high rate, overcharge is not tolerated well. A missed delta will often cause damage.

In my experience, packs always charged at C/10 or less will have a longer life span than packs charged on a peak detect charger. I realize this is contrary to Battery University. I suspect (just my opinion) that Buchmann is more interested in promoting his company than in being completely honest.

Unknown, I don't understand the distinction you are making. When a cell is fully charged it will dissipate any further charge energy as heat. This is an indication that the cell is fully charged. At low charge rates the heat is not damaging to the cell. This is why Sanyo and other manufacturer's state a standard timed charge rate at C/10.

On the other hand, cells can be damaged by use of an unreliable peak-detect charger. Because peak detect chargers charge at a relatively high rate, overcharge is not tolerated well. A missed delta will often cause damage.

In my experience, packs always charged at C/10 or less will have a longer life span than packs charged on a peak detect charger. I realize this is contrary to Battery University. I suspect (just my opinion) that Buchmann is more interested in promoting his company than in being completely honest.


Unknown, I don't understand the distinction you are making. When a cell is fully charged it will dissipate any further charge energy as heat. This is an indication that the cell is fully charged. At low charge rates the heat is not damaging to the cell. This is why Sanyo and other manufacturer's state a standard timed charge rate at C/10

The very fact that it is a timed charge is proof that the heat is damaging to the cell - why else have such a solid cut off ? Clearly, Sanyo are aware that to charge for longer WILL damage the cell. It's a low key budget attempt at not overcharging fully discharged cells and makes no allowances for loss of capacity or partly discharged cells.

A Nimh cell can only dissipate so much heat, temperature is not an indiction of state of charge, whereas rate of temperature change is.

So, anyone who believes that checking if a battery is 'warm' (in relation to what?) to ascertain charge state is sorely mistaken.

I said earlier
While these are all bad things - Nimh do not like being trickle charged - I believe cheap fast chargers are more damaging.I also believe cheap fast chargers (and even some that are not so cheap) are damaging.

When charging a single Nimh cell I select a C rating and monitor the temperature and delta peak - or rather my charger does. I do not own, use or recommend a Buchmann charger. :)

You seem somewhat confused on some basic facts:
Because peak detect chargers charge at a relatively high rate, overcharge is not tolerated well.Different types of chargers use delta peak detection not just fast chargers. In fact, the delta peak is easier to detect with higher charge rates. A fast charger is not necessarily using peak detect.

You seem somewhat confused on some basic facts: Different types of chargers use delta peak detection not just fast chargers. In fact, the delta peak is easier to detect with higher charge rates. A fast charger is not necessarily using peak detect.

Right. A peak detect charger needs to have a relatively high charge rate in order to obtain a discernible peak. Peak charging at C/10 is not generally done because the voltage inflection is too small. Because relatively high rates (compared to C/10) are used, a missed peak can be a problem. Overcharging at C/10 is not a problem. Overcharging at C or C/2 or C/3 IS a problem.

The very fact that your charger has two detection methods should tell you something. If peak detect alone were completely reliable then the temperature sense would not be needed. If overcharging because of a missed peak were harmless then temperature sense would not be needed.

Right. A peak detect charger needs to have a relatively high charge rate in order to obtain a discernible peak. Peak charging at C/10 is not generally done because the voltage inflection is too small. Because relatively high rates (compared to C/10) are used, a missed peak can be a problem. Overcharging at C/10 is not a problem. Overcharging at C or C/2 or C/3 IS a problem.

The very fact that your charger has two detection methods should tell you something. If peak detect alone were completely reliable then the temperature sense would not be needed. If overcharging because of a missed peak were harmless then temperature sense would not be needed.

And by your own argument, if the temperature/temp change sensor were reliable by themselves, there would be no need for peak detection.

Anyways, doing some more reading (http://www.mpoweruk.com/chargers.htm), it would seem that multiple cut-offs are used in universal chargers for various reasons, not least because...

Negative delta V (NDV) Cut-off charge system

This is the most popular method for rapid charging for Nicads.

Batteries are charged at constant current of between 0.5 and 1.0 C rate. The battery voltage rises as charging progresses to a peak when fully charged then subsequently falls. This voltage drop, -delta V, is due to polarisation or oxygen build up inside the cell which starts to occur once the cell is fully charged. At this point the cell enters the overcharge danger zone and the temperature begins to rise rapidly since the chemical changes are complete and the excess electrical energy is converted into heat. The voltage drop occurs regardless of the discharge level or ambient temperature and it can therefore be detected and used to identify the peak and hence to cut off the charger when the battery has reached its full charge or switch to trickle charge.

This method is not suitable for charging currents less than 0.5 C since delta V becomes difficult to detect. False delta V can occur at the start of the charge with excessively discharged cells. This is overcome by using a timer to delay the detection of delta V sufficiently to avoid the problem.

dT/dt Charge system

NiMH batteries do not demonstrate such a pronounced NDV voltage drop when they reach the end of the charging cycle, and so the NDV cut off method is not reliable for ending the NiMH charge. Instead the charger senses the rate of increase of the cell temperature per unit time. When a predetermined rate is reached the rapid charge is stopped and the charge method is switched to trickle charge. This method is more expensive but avoids overcharge and gives longer life. Because extended trickle charging can damage a NiMH battery, the use of a timer to regulate the total charging time is recommended.