NiMH new battery conditioning

"Jeff Liebermann"

I would never mistreat NiMH AA cells the way you just have.

A 1C discharge test will never give the rated capacity figure with NiCd or NiMH.

IME - the idea that new cells have a "running in "period is a MYTH invented by retailers back in the 1970s when consumers were first sold AA and C size NiCds and found their performance disappointing when compared to alkalines.

The inherent lower terminal voltage and cell mAH capacity were the real reasons.

.... Phil

Yep. I don't like them.

I didn't have time to do it the right way (20 hr discharge). I can do it again with a longer discharge time and lower current. I still have several of both brand of cells that I haven't mistreated yet. However, it will take about a week to produce results (plus dragging home a spare computah to do the test and building a better battery holder).

True for the Duracell, which recommends 205ma for 15 hrs to recharge printed on the cell. The Energizer Recharge battery doesn't specify a charge current:

However, the recommended battery charger is a quick charger:

with a 15 minute charge time.

I've been testing batteries since about 2005 while working on a product that I won't discuss. However, I will point out that many NiCd batteries can be quick charged at ridiculously high rates, as long as certain (unspecified) conditions are met. If you don't mind, I'll leave this unsubstantiated.

Incidentally, the Sanyo ENELOOP battery data sheet recommends fast charging at 2A for 1.1 hrs:

I indicated that in my posting as:

The purpose of the test was to see if a brand new battery required several charge-discharge cycles before it would deliver full capacity, not to measure the actual rated capacity in a 20 hr discharge test.

Maybe. There was also quite a bit of effort in the mid 1990's by manufactures to differentiate their NiMH products from NiCd. For example, I found a pair of Lenmar NoMEM Pro NiMH batteries, which are an obvious shot at the alleged NiCd "memory effect". Another possibility is that some support droid needed a line to get rid of a complaining customer and invented the "conditioning" for the purpose.

Agreed. I went through the mess with alleged "9V" (6 cell) NiCd batteries, being more like 7.2VDC. With a nominal operating voltage for 1.2 to 1.3 VDC for NiCd and NiMH, anything designed for a 1.5VDC alkaline is going to have a problem.

Incidentally, all of the marine radios I helped design were required to function down to 10.0VDC applied power. They couldn't reach rated TX power at 70% of rated voltage, but still had to belch at least a few watts of RF and remain functional.

I'm rather mystified by the results. Although the improvement in capacity after 3 charge-discharge cycles is minor (10-15%), it still seems for real. My previous tests didn't show such an increase in capacity. Instead, it showed a deterioration in capacity. However, I was testing for something quite different, and was working with a mix of old and new cells.

Though it is possible to charge an eneloop battery in a "Quick Charger", it is not recommended. We recommend charging eneloop batteries in a NiMh charger that is 2 hours or more. Charging eneloop batteries in a "Quick Charger" can reduce the overall life of the battery. I've read statements to the effect that one reason you would want to use moderately-fast charging rates (e.g. 1C) rather than the low rates traditional for most NiCd cells (e.g. 0.1C), is that the NiMH cells will heat up more abruptly when they reach full charge, and the charging power starts turning into heat rather than electrochemical potential. The abrupt rise in cell temperature is easier to detect reliably (via a temperature sensor and/or due to the zero-delta-V effect) than if you were charging more slowly... and thus a more reliable "full charge, stop now!" shutoff circuit can be designed, and avoid overcharging (which I understand NiMH cells don't tolerate at all well).

A good decision! It bothers me that a lot of HF and VHF radios "poop out" at much below 12 volts.

For what it's worth, the Sanyo FAQ page cited above does make reference to the break-in effect:

Should I store my batteries charged or uncharged? If stored with charge, it is possible that when you return to use the battery there may still be some charge left in the battery, therefore it will enable you to use it right then and there. Also, by keeping some charge in the battery, it will require you to "cycle" the battery fewer times until it reaches its peak charge. If you store them with no charge, you will have to "cycle" the battery multiple times until it reaches its peak charge.

A two-hour charge is, by any reasonable standard, a "quick charge". It would be at least 0.5C -- hardly a slow charge.

"William Sommerwanker"

Quick chargers deliver about 0.2C to 0.5 C

Fast chargers deliver 1C to 4C ( ouch ! )

Because NiMH ( AA, A or 9V ) cells vary widely in rated capacity - the same charger has multiple rates.

So called " simple " chargers have a timer as the only cut out.

A 4C fast charger that only has a timer is a lethal weapon.

IME - the worst offenders in supplying chargers that are practically guaranteed to ruin the cells are the battery makers - ie Energiser, Varta and Sanyo.

Funny about that.

.... Phil

I thought you'd reformed. But you haven't. Why don't you just go back to being a foul-mouthed jerk? That's what you want, isn't it? You want people to hate you, because it makes you feel superior.

The worst part is that when you aren't making nasty remarks, you almost always have somthing worth hearing.

Our own little Eric Cartman. How charming.

As they sell batteries, why should it be funny?

Based on my experience at Microsoft Hardware, and MAHA's documentation, 0.1C is not considered an appropriate charge rate for NiMH cells. Higher rates are recommended, supposedly because they pump more charge into the cell before the cutoff voltage or temperature is reached.

I rarely charge faster than 0.3C. That's just basic cowardice on my part.

"William Sommerwanker = Colossal FUCKWIT "

Not to mention being contrary to consumer law.

For * loose cells * sold to the public and in the absence of " smart " chargers that treat each cell as in individual - it is the only reliably safe method.

A whole different ball game.

BTW:

Ruining refers to a simultaneous loss of capacity and LARGE increases in self discharge rate and internal resistance.

.... Phil

Not for me. I own two smart chargers.

See preceding.

Like the alleged increase in NiMH capacity produced by initially "conditioning" the battery, there's the question of how much does quick charging a battery reduce its overall life? According to various documents which I'm too lazy to find, a cell is considered dead when it reaches 50% of its rated capacity. One text mumbled that quick charging will reduce the number of charge cycles by 20%. For a

My guess(tm) is that internal heating is doing the damage. With a defacto standard 16r 0.1C charge, there's some excess power going into heat. For a perfect battery, 10 hrs of this 0.1C is all that's required to get to 100%. The other 6 hrs of charge is going somewhere, most likely into heat. Over a 16 hr charge, that's not going to heat up the battery much. Over a 0.25 hr 4C charge, that's quite a bit of power heating the battery. Note that the internal resistance (ESR) of the battery also heats the battery on discharge, making a rapid discharge risky.

So, why the wide variation in capacity and recommended charging methods? Because none of them will satisfy everyone. If you ask marketing, they will offer the highest possible science fiction capacity, over unrealistic discharge times (20 hr), with the fastest possible (4C) recharge because that's what consumers want. If you ask the company legal counsel, they will offer a much lower capacity to avoid getting sued, and the safest possible recharge method, for the same reason. Everyone lies, but that's ok because nobody listens.

The problem is that I don't have the time to run a proper test. I could take one of the brand new Energizer cells, charge at 4C (15 min), discharge at 1C (about 45 min), and repeat as many times as it takes for the battery capacity to drop 50% from 2300 ma-hr. Without automation, my guess is that I can do about 4 cycles per day. That will take 3 months before I kill the battery.

Sorta. The amount of heat (calories) produced by fast or slow charging is the same. However, with fast charge, the heat is produced over a much shorter period, resulting in a much higher cell temperature. Methinks it's this temperature that kills the cells.

Incidentally, I learned the hard way with NiCd batteries that once the heat gets to the case and is able to be measured, it's too late. The internal damage is already done. Internal sensors are required.

Note the magnetic temperature sensor on my battery fixture (that has fallen off and landed on the spring).

Yep. Quick charging will produce a higher cell temperature which is easier to detect.

During my experiments with NiCd batteries, I've found that I can charge a single cell at almost any rate (I've done 20C). As long as the battery is below 100% capacity, there is almost no heating. As the battery approaches about 95% of capacity, the heating starts, and rapidly increases. I've quick charged 650 ma-hr NiCd batteries to almost full charge in about 3 minutes. However, there's a catch. If I miss the 95% point, and go over, the overcharge will either kill the battery, or vent boiling caustic electrolyte. It's for this reason that I suspect really quick chargers are not sold or recommended. I have not done any such testing with NiMH.

Fishing boats like to run quiet, with the engine off. There are also sailboats and small boats that only charge the battery at the dock. (These daze, they have solar chargers). It's not unusual for them to use crappy batteries, that have a no charge terminal voltage of

Note the misuse of the words "peak charge". It should say "peak capacity". Kinda reads like this was written by marketeering, not engineering. If they had mentioned that ignoring this sage advice might result in an initial loss of 10-15% of peak capacity (per my tests), I suspect that users would probably ignore the problem. However, because the effect is not innumerated, it looks a major problem.

So, if I cycle a new NiMH battery with a 4C charge, and a 1C discharge, how many cycles would you guess I would get before the battery hits 50% of rated capacity? The winner gets what's left of the test battery (suitable for recycling) when I'm done.

That kinda begs the question if submerging the cell in cooling water will allow for a fast charge (4C) without overheating and killing the battery? I can see it now... the super-fast battery charger, just add coolant.

Several years ago I ran tests using name-brand AA alkalines and 2500mAh NiMH cells to power a STAX headphone amplifier. (This was not completely valid, because I had no idea what the alkaline cells' rated capacity was. Does anybody know?)

Much to my surprise, I discovered that the rechargeable cells powered the unit as long as the throwaways. This means I'd break even after only 10 recharges. Even if I was off by 50%, I'd still need only 20 recharges.

The shortened life of fast recharging has to be weighed against the cost of using throwaways. In practice -- particularly with heavy-drain devices -- you don't need many charge/recharge cycles to break even.

This is why I carry multiple sets of NiMH cells for my flashes and other heavy-drain devices. With multiple sets, I don't have to worry about rapid recharging, and can stick with 0.2C or 0.3C.

It varies radically with load. With a very light load, it's as high as 2000 ma-hr. With a heavy 1 amp load, as little as 550 ma-hr. However, even that's not consistent. I was comparing Costco Kirkland alkaline AA batteries, with the equivalent Duracell, Ray-o-Vac, etc cells. The cheapo Kirkland cells were far better with a 1A load, but sucked with a light load. Duracell was the exact opposite. The differnces were not huge, but they were reproducable.

More than you ever wanted to know about alkaline batteries:

Note the variations by brand and type and the NiMH cell in the bottom graph.

Headphone amps sound like a light load. Got a number for the average current drain?

I killed a small Canon camera by using alkalines. It was apparently designed for the normal terminal voltages found with NiCd and NiMH. When I stuffed in an alkaline cell, the camera overheated after about

Also, NiMH can handle short duration high current loads much better than alkaline. That's they type of load found in many digital cameras. Alkaline might be an option for a low current load such as your headphones, but they wouldn't last long in a high current camera.

I've had problems with self discharge in previous NiMH batteries. So, I have a 117VAC/12DC fast (4C / 15 min) charger in the camera bag. When I need to shoot lots of photos, I give it a quick charge. Maybe the LSD (low self discharge) NiMH will eliminate this problem.

More on how NiMH charging:

-- Jeff Liebermann snipped-for-privacy@cruzio.com

The operative word here is STAX -- as in high-voltage electrostatic earphones. I never measured the drain, but neither set of cells lasted much more than four hours.

rapid

We still don't have a rational answer as to why some people don't have problems with rapid self-discharge.

I don't shoot every day, so I can charge-up the night before. I have two chargers, which makes things easier.

$2,000 for earphones and you're worrying about the price of rechargeable batteries? Argh.

There seems to be two amps. One with tubes and the other presumably IC's.

Oh, that's easy. How many charge cycles would you guess you get on a set of NiMH before they're ready to recycle? You probably don't know and neither does Joe Sixpack. I don't even know because nobody is counting. So, Joe Sixpack may get 2 years of service out his NiMH battery pack, but has only charged it perhaps 20 times before it died. I vaguely know someone that maintains TV camera battery packs for one of the major networks. Current technology is Li-Ion but in the not so distant past, it was NiMH and NiCd. He keeps meticulous records. I must admit that I wasn't paying attention when he showed me the numbers, but it seemed to me that even for identical battery packs, the numbers were almost random. Some would last on a few charge cycles, while other would last seemingly forever. He attributed this mostly to depth of charge and storage temperature. Even the best battery, stored hot, will die prematurely. This is a known problem with Li-Ion, but I'm not sure if storage temperature has any effect on NiMH. Mine are all in the fridge, just in case. Depth of charge is the biggie. A battery that is only discharged to perhaps 75% of full charge, can be charge cycled many more times than one that is fully discharged before recharging. However, if the charger is too aggressive, a battery that's discharged to 75% might be overcharged, while the one that's fully discharged is less likely to be overcharged.

I have 3 fast chargers. House, office, and vehicle. The one in the vehicle seems to get the most use.

No, they were more like $350. I said earphones, not headphones.

Wrong units. This is a pocket-sized transformerless energizer that runs off two AA cells. It works with a tiny pair of electrostatic earphones.

That's extremely useful information, but I'm still not sure it answers the question -- unless you're suggesting that the people who have problems with rapid self-discharge have damaged their cells.

Pardon my ignorance, but what is the difference between earphones and headphones? I use the terms interchangeably.

Nope. A one line summary would be that most users don't remember how many times they have charged their NiMH cells, don't recall how old they are, and have no clue as what constitutes normal lifetime. If someone has a battery killer in the form of a battery charger, they would just continue to use it, killing battery after battery, without ever doing the math needed to determine if something is wrong.

Even simpler... do *YOU* record the number of charge cycles of your rechargeable batteries? If not, then you have no accurate way to determine if you're getting the normal number of charge cycles (400-800) from the NiMH batteries (unless you have a really good memory).

Headphones sit on your head. Earphones go in your ears. Sennheiser 600s are headphones. Etymotics are earphones.

the

That makes sense. However, the question was about rapid self-discharge -- NOT the total number of charge/discharge cycles.

None of my NiMH cells has had gone through more than 100 cycles -- most a lot less.

Again, the issue is "rapid" self-discharge. I don't see where the gradual loss of capacity necessarily results in more-rapid self-discharge.

The complaints about NiMH cells were with respect to nicads. I'm assuming (perhaps incorrectly) that the plaintiffs were comparing relatively new NiMH cells with older nicads -- which should have been in worse condition, and therefore subject to more-rapid self-discharge.

My experience with newer NIMH high capacity cells indicates that their capacity improves considerably, after at least several charge/discharge cycles. If I hadn't been aware of the NIMH chemistry's low initial capacity before I purchased them, I would've been seriously disappointed at their initial test results.

I've also seen, but not tried, cells that are claimed to be pre-conditioned.. so they're supposedly ready for use after the first charge.

My testing was controlled, and didn't perform any deep discharging, like that which could happen with a cordless power tool, for example.

The cells I'm presently using are Powerizer 4500 mAh sub-C cells (in packs of 5) and Tenergy 10,000 mAh D cells (also in packs of 5).

For the first couple of cycles, the capacity is about 50% and gradually improves to full capacity after 5 or more cycles (at reasonable rates). I'm using 1A charge rate for the 4500, and 2A for the 10k packs now.. although I wouldn't consider higher rates of 2A and 4A to be detrimental, as long as the cells don't heat up.

The MRC Super Brain 977 will provide a reading for the discharge mAh, and prevents damaging deep discharges. Readouts will include rate, time and mAh.. so test results can be noted and compared. Charging and discharge rates are completely adjustable, which makes this model fairly versatile.. and it can be input with vehicle 12V for charging packs of less than 12V.

I also bought a MRC 992, which has a port for a USB cable (which I don't have), and since the 992 doesn't have the discharge capability, I don't care much about plotting charging cycles.

Sophisticated chargers can detect problems in charging rates and then shut down, but less advanced chargers will continue to supply charging current.

I have experienced fault Errors with both of the MRC units, which I consider a valuable feature.. there were 2 questionable older AA cells in the 4-cell holder, and I'd marked those 2 cells previously becaue they had elevated temperatures when charged with a different charger in the past.

I also have some negative-pulse chargers which continuously monitor the state of charge. For these chargers, I just write the begin time on a sticker, to see how long the packs have charged when they're finished.

Another handy item is a continuous rate discharging unit, made for cycling commercial ENG camera batteries, as part of a conditioning cycle. Anton Bauer ADM is a 2A rate for 12-14V packs.

As mentioned numerous times in the past, there are many different grades of cells, and certain cell types have specific features that the others don't. Traditionally, the best quality rechargeable cells are from Japan, and those cell makers provide lots of specifications for their products.

I'm convinced that overheating cells is damaging, and precautions should be taken to prevent overheating. Unattended charging is generally high risk, as many battery pack temperature cutouts are rated so high (65 C), that by the time the air in the plastic housing reaches the cutout temp, the core temps of the cells are already beyond a safe/reasonable range.

-- Cheers, WB .............