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    Exclamation Cycle Testing Observations…

    Cycle Testing Observations…

    I have had several discussions about how batteries age during their use. Winny was so kind as to translate an article on battery cycle testing for me (many thanks Andreas), and I decided to see if I could answer some questions that I have had.

    Cycle testing takes a large commitment of time and equipment. There is not a fast way to do this, and commercial equipment is designed around “standard” parameters that do not necessarily reflect the way we use our batteries.

    I have been told that fast charging reduces cycle life, however I have been unable to get any specific numbers. This became the objective of this test.

    I took two Sanyo 2500 mAh cells, performed a forming charge of 200 mA for 16 hours, cycled them 5 times, and proceeded with the testing.

    Two chargers were compared. The Energizer 15 minute charger was the fast charger, and the Sanyo NC-MQH01U was used as the slow charger by utilizing one of the slow charge slots. The Sanyo charger charges at roughly a 1.0 amp rate in that slot.

    The first test was done after charging both cells on the slow slots of the Sanyo charger. This became my base line capacity. The cells came out reasonably close in capacity and the testing continued.

    I saved the data collected every 25 cycles, and it is presented below.

    The procedure involved charging the cell on its respective charger, letting it rest for 20 minutes, then discharging it at 2.5 amps down to 0.8 volts.

    High capacity cells are not the best choice for high charge or high discharge rates. A cell is usually considered fully discharged at 0.9 volts, and going to 0.8 volts is a bit of an over discharge. These values were chosen to accelerate the aging process and reduce the number of cycles needed to see a trend. I also only let the cells rest when I was asleep. I believe you can get improved life by less rigorous usage.

    A general consensus from a variety of battery manufacturers suggest that you can expect around 500 cycles from high capacity batteries, and around 1000 cycles from lower capacity batteries. Lower capacity batteries are those with less than 2200 mAh of capacity, however Energizer was the only one that suggest a 2200 mAh cell as lower capacity. Most consider 2000 mAh cells as the high end of the lower capacity cells.

    Keep in mind that when the battery manufacturer comes up with these numbers, they are doing a 5 hour discharge and a 14-16 hour slow timed 0.1C charge.

    Also, keep in mind that all of the information I have been able to find indicates the number of cycles to reach around 60-80% of the cells original capacity. It is understood that the mid point voltage will be reduced, but the performance is measured in reduction of capacity.

    In non regulated flashlights, the voltage retention under load is very important to the brightness of the light. It has been interesting to watch the voltage drop during cycling.

    Here is the data from the slow charge through 150 cycles.



    Here is the data from the fast charge through 150 cycles.



    Here is a comparison of the slow charged cell at 125 cycles with the fast charged cell at 100 cycles. Based on this limited testing, it looks like you lose around 25 cycles by fast charging.



    In my notes I observed that the fast charge cell was about done after 125 cycles. I then switched to “topping off” the fast charge at a slower rate on the Schulze charger. This did not seem to have much effect.

    At 148 cycles, the fast charge cell was no longer able to be charged on the Energizer 15 minute charger. I would put the cell in, and would get a blinking red error light. The final charge cycles were done on the Schulze.

    Out of curiosity, I did another cycle (number 151) on both cells. This time I charged both cells on the Sanyo charger and did the discharge at 1.0 Amps.



    Conclusions:

    Fast charging high capacity cells, followed by fast discharging to an over discharged state is harder on the cells than slow charging followed by the same conditions.

    The mid point voltage drops with use and it seems to drop faster with fast charging.

    Cycle performance based on a percentage of remaining capacity does not tell the whole story.

    Cells stressed and damaged by heavy usage may still be suitable for lower drain applications.

    The performance lost by cycling is permanent.

    There does not appear to be an increase in the self-discharge rate of high cycled cells.



    Here is round 2 of this effort. I was wondering how smaller capacity cells would handle this. I took some Titanium 2000 mAh cells and decided to test them under the same conditions. The same chargers were used, and the discharge remained at 1C, which, in this case is 2.0 amps.

    I did change one thing. After 50 cycles, I decided to do a 0.1C charge for 16 hours after every 25 cycles. These cells seemed to be able to handle the cycles a lot better than the higher capacity cells did. I am not sure if the forming charge made any difference or not.

    There was no problem charging on the Energizer 15 minute charger, and while the cells have lost some capacity, they still seem to be in reasonable condition.

    Here is the data from the slow charge through 150 cycles.



    Here is the data from the fast charge through 150 cycles.



    Here is a comparison of the slow charged cell at 125 cycles with the fast charged cell at 100 cycles. Based on this limited testing, it looks like you lose around 25 cycles by fast charging. This is the same result that we saw with the Sanyo 2500 mAh cells.



    Once again, I did another cycle (number 151) on both cells. This time I charged both cells on the Sanyo charger and did the discharge at 1.0 Amps.



    Conclusions:

    Lower capacity cells handle cycle testing better than higher capacity cells.

    Lower capacity cells handle fast charging better than higher capacity cells.

    It seems that fast charging performance drops off faster than slow charging performance, buy around 25 cycles.

    Based on this limited amount of testing, I can believe that these cells may be able to go 300-500 cycles. Looking at the data from the 1.0 amp discharge at cycle 151, the slow charged cell is at 95% of the original Amp Hours and 91% of the original Watt Hours. The Fast charge cell is at 94% of the original Amp Hours and 88% of the original Watt Hours. Cycle testing usually goes to 80% of the original Amp Hour capacity, so these cells still have a ways to go.

    It would appear that the price you pay for higher capacity is a loss of power and cycle life. Of course, this test is designed to accelerate the process. Charging and discharging at lower rates may give you some additional cycle life.

    Round 3

    This time the testing involved Sanyo Eneloop cells. These cells have a low self discharge rate and are supposed to maintain about 85% of their initial capacity after a year of room temperature storage. These cells may be sensitive to extended trickle charging as well as high charge rates.

    These 2000 mAh cells were charged on the Energizer 15 minute charger which uses a 7.5 amp charge rate. That works out to charging at around 3.75C. Discharging was done at 1 amp this time, and every 25 charge/discharge cycles a 16 hour charge at 200 mA was done.

    It was interesting to observe the performance of these cells. They started out having an internal resistance of 0.026 ohms. They held, or slightly increased in capacity over the first 100 cycles, then they started to fade. Looking at the graph you can see this fade in cycles 125 and 150.

    I then charged them back up and let them sit for 30 days. It appears that this ultra rapid charging has effected the cells ability concerning low self discharge. Also, the cells internal resistance rose to 0.340 ohms. Discharge 151 on the graph has a very interesting shape to it. The Energizer 15 minute charger now rejects these cells. When I charged them up and put them into my camera, I got a low battery warning after 15 shots. I was able to coax another 8 shots before the camera powered down. I usually get several hundred shots from a set of Eneloop cells.

    It looks like these cells can handle 100 – 125 charge cycles on the Energizer 15 minute charger, but after that they are about done. The Titanium 2000 cells came in better than these cells did, but they are not low self discharge. Overall, I was impressed that they held up as well as they did, but for longer cycle life it would be better to keep the charge rate in the 0.5 – 1.0C range.

    Here is the graph.




    Tom
    Last edited by SilverFox; 06-16-2008 at 06:05 PM.
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  2. #2
    Flashaholic* JimH's Avatar
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    Default Re: Cycle Testing Observations…

    Tom,

    Fantastic report . That sure looks like a whole lot of work. How many months did it take to run through all those cycles?
    Jim - Have lights, lead, and steel will travel

    The heck with runtime. I just want to hold the sun in my hands!! Brighter is Better!

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    Default Re: Cycle Testing Observations…

    So much for the 500 cycle claim, unless they aren't designed for the 3 amp discharge rate. I guess I should stop refreshing my batteries every so often, I'm just killing the cycle life.

    By the way, what is it with the last set of graphs looking like a hill. The voltage actually went up during testing?

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    Default Re: Cycle Testing Observations…

    hello silverfox

    excellent work as usual.

    I think the sanyo 2500 did very well after 150 cycles in 15 min charger at 7.5 amps.

    I am more suprised at the capacity loss on the slow charged battery`s of 228mah compared to the new cell.

    unless you have a hard to find, or expensive battery pack.

    it looks like fast charging is the way to go.

    regards.
    "Build a man a fire, and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life." - Terry Pratchett.

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    Default Re: Cycle Testing Observations…

    Quote Originally Posted by bcwang
    So much for the 500 cycle claim, unless they aren't designed for the 3 amp discharge rate. I guess I should stop refreshing my batteries every so often, I'm just killing the cycle life.
    I too wonder about frequent refreshing or "topping off", but I'm not sure this particular test helps out in knowing whether this is a good practice, since the use pattern is pretty extreme.

    I recently acquired a new Lux V bike light that uses 4 AA NiMH's. The light has a low battery indicator that comes on at about 1 hr. 40 mins. However, at that point the cells still indicate 1.2 v (with no load). Silverfox--do you how much recovery is normal, i.e., what voltage cells discharged to 0.8 v read after a rest period of say an hour?

    I want to thank you for all the work you've put into this, and other similar projects. Based on your initial reports, I bought the Energizer 15 min. charger, since there are times I just can't wait a couple of hours for cells to be topped up. I'm still very happy with the purchase, even though it's not as gentle as a slow charger.

    Jack

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    Default Re: Cycle Testing Observations…

    Hello Bcwang,

    Keep in mind that the results are for 100% depth of discharge cycles. I believe that if you re-charge frequently, the actual number of cycles goes up exponentially.

    I saw the "hill" several times. It seems that under this load, the cell recovers slightly when the chemistry heated up. I found it very interesting...

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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    Default Re: Cycle Testing Observations…

    Hello Jack,

    Until the last few cycles, both of these cells recovered to 1.18-1.20 volts after the discharge cycle.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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    Default Re: Cycle Testing Observations…

    Thanks Tom - Great work.

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    Default Re: Cycle Testing Observations…

    Hi Tom,

    This post is important. Thank you for posting your findings.

    vince.
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    Default Re: Cycle Testing Observations…

    Tom:

    Nice work Tom! The only thing that I question is in "realtime" use .8V/.9V is below the level that a battery powered whatever may show a low battery. I've only check two things so far, a Fluke 189 DMM and a RS Pro 94 scanner. The scanner started beeping low battery at 1.15V per cell and the the DMM was 1.12V if my memory serves me correctly. Of course your tests are full cycles but I wonder how this same test would fair with a 1.1V cutoff?

    EDIT: Corrected voltage typos.
    Last edited by wptski; 04-18-2006 at 09:24 AM.
    Bill

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    Default Re: Cycle Testing Observations…

    Wow Tom, outstanding work. It must have taken an enormous amount of time running these tests and compiling the data. Thanks for doing this.

    Paul

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    Default Re: Cycle Testing Observations…

    Hello Bill,

    I am not sure how much influence discharging to a lower voltage had on the cycle life of the cells. They would usually rebound to around 1.2 volts after the test.

    I believe your applications are drawing less current and using more than one cell. If I were checking a pack, I would stick to a 1.0 volt cut off.

    At any rate, I chose the lower cut off in an effort to accelerate the test. I really didn't want to spend all my time testing... There are flashlights to play with... oops I mean use.

    Testing is done to answer questions. However, in the course of conducting the tests, it seems like a whole new group of questions arise. This test was no exception.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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    Default Re: Cycle Testing Observations…

    Quote Originally Posted by SilverFox
    Hello Bill,

    I am not sure how much influence discharging to a lower voltage had on the cycle life of the cells. They would usually rebound to around 1.2 volts after the test.

    I believe your applications are drawing less current and using more than one cell. If I were checking a pack, I would stick to a 1.0 volt cut off.

    At any rate, I chose the lower cut off in an effort to accelerate the test. I really didn't want to spend all my time testing... There are flashlights to play with... oops I mean use.

    Testing is done to answer questions. However, in the course of conducting the tests, it seems like a whole new group of questions arise. This test was no exception.

    Tom
    Tom:

    Gosh! Bigtime typos above! That should be 1.15V and 1.12V per cell.

    Yes, my applications do draw less current but does that matter? Often as seen in your Ni-MH shootout thread, discharge capacities hardly varied much between .5A and 1A. I wonder how much capacity varies between .9V and 1.1V? The discharge voltage on any charger is based on cell count wether it's auto/manually.
    Bill

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    Default Re: Cycle Testing Observations…

    I've done plenty of discharge tests manually with a current load and DMM, and have watched the voltage change over the discharge curve. 1.1V to 0.9V happens in only a few minutes during a 0.5C discharge test. In reality, the added runtime from discharging to 0.9V isn't worth the risk of reversing cells, especially in larger packs.

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    Default Re: Cycle Testing Observations…

    now to see what the reduction in capacity is caused by.
    perform a flash amps test on a set of 3 cells.
    1 new,the high rate,and the low rate.
    or test with an esr meter if you have one.
    post results.
    a more controlled test would have done this at the start but a new unabused/cycled cell is a decent control if its from the same batch.

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    Thumbs up Re: Cycle Testing Observations…

    Thank you so much for kindly sharing your knowledge with us...always carefully tested and right up to date, too.

    I can't help wondering whether Rayovac IC3 batteries, using their 15 minute charging system, would show similar results.

    I've noticed there is now another proprietary 15 minute charger here in Canada, under the Noma brand name.

    With Rayovac discontinuing theirs, do you know if the Noma batteries might be interchangeable?

  17. #17

    Default Re: Cycle Testing Observations…

    Quote Originally Posted by bcwang
    So much for the 500 cycle claim, unless they aren't designed for the 3 amp discharge rate. I guess I should stop refreshing my batteries every so often, I'm just killing the cycle life.

    By the way, what is it with the last set of graphs looking like a hill. The voltage actually went up during testing?

    Sanyo Twicell design sheet shows capacity is beyond initial capacity after 100 cycles and drops to 80% after around 430 cycles based on C rate charging(-10mV termination) 1h rest, C rate discharge, 1h rest... and repeat.

    Their end of discharge votlage was 1.0v. Silverfox used 0.8v.

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    Default Re: Cycle Testing Observations…

    Quote Originally Posted by Handlobraesing
    Sanyo Twicell design sheet shows capacity is beyond initial capacity after 100 cycles and drops to 80% after around 430 cycles based on C rate charging(-10mV termination) 1h rest, C rate discharge, 1h rest... and repeat.

    Their end of discharge votlage was 1.0v. Silverfox used 0.8v.
    Wow, if .8v vs 1.0v makes that much of a difference, I'd better charge my batteries early. Some of my devices can easily bring down the voltage below .8 before the device dies. I wonder if the .9v used by the lacrosse hurts cycles any worse than using 1v as the termnation point.

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    Default Re: Cycle Testing Observations…

    Hello Handlobraesing,

    I am not sure what data you are looking at, but I was only able to find information for the HR-4/5AU cells. These cells are rated at around 2100 mAh, and should perform differently than the 2500 mAh high capacity cells.

    It seems that once you get over 2000-2200 mAh capacity, things change.

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

  20. #20

    Default Re: Cycle Testing Observations…

    Tom,
    http://www.sanyo.com/batteries/pdfs/twicellT_E.pdf is the paper I'm talking about.
    In the charging method, it says:
    "Set the charge current at a value between 0.5It and 1It.*** during quick charging"

    As an exception, they define maximum charging current for HR-4/3AU and HR-4/3FAU as 3.0A.

    A few sentences below, it says "If charging is performed at a current exceeding the maximum allowed current (1It), the rate of oxygen gas consumption at the negative electrode will not keep up..."

    Sanyo uses "It" to refer to the charge rate and it means the samething as "C" that is more commonly used.

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    Default Re: Cycle Testing Observations…

    Tom,

    Fantastic work as usual! Thank you so much for all of the info that you selflessly provide to us. It has been invaluable to me on more than one occasion (as you know )

    I assume that when you say "It seems that once you get over 2000-2200 mAh capacity, things change" that you are talking about AA cells only, right?

    Because a 2000 mAh sub-C NiMH would definitely be a LOW-capacity cell, and a 2000 mAh AAA cell would be incredibly HIGH-capacity. My point is too obvious to belabor further. Unless I'm wrong, of course, and then please feel free to belabor it.

    Anyway, Tom, really, THANK YOU for this. Incredible information and very enlightening and revealing. I never would have thunk it.
    -Jim Sexton, creator of the M6-R, the TigerLight Upgrades, Fixture-ring lamp potting, the SL60, co-designer of the B90 Upgrade, and proponent of the SF A2, the SF M6 X-LOLA, Titanium, the Haiku, and the LunaSol 20

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    Default Re: Cycle Testing Observations…

    look at this
    New Products

    Vapex Offers New VTE2000AAP NiMH Battery

    January 15, 2004



    Vapex Technology Ltd. (Hong Kong) unveiled its new VTE2000AAP rechargeable nickel-metal hydride (NiMH) battery, which has a high energy density that is 15% over the normal 1,800mAh battery, a high drain performance of up to 3C, and a high shelf life that is 80% of the initial capacity storage for two years.


    WHAT do you say ? Anyone has it ?

  23. #23

    Thumbs up Re: Cycle Testing Observations…

    First thanks for the effort, we appreciate it.

    Quote Originally Posted by SilverFox
    Two chargers were compared. The Energizer 15 minute charger was the fast charger, and the Sanyo NC-MQH01U was used as the slow charger by utilizing one of the slow charge slots. The Sanyo charger charges at roughly a 1.0 amp rate in that slot.....

    Tom
    I am bit puzzled by your terminology. I would call the 15 min charger "super-fast" and the Sanyo @ 1 / 2.5 = 0.4C a "medium speed". I thought that 0.1C (250mA) used for the forming stage is a "slow speed". Not to split hair, the reason I bring this up is that some people prefer longer cell life to 15 min convenience. For instance, I simply have a set of backup Alkiline cells for the times when I am in a rush and just don't bother with "super-fast" or even "fast" speeds.

    When I got my BC900 I used the default 200mA rate - "slow". Due to the issues brought up here I switched to 500mA rate which is still "slowish" according to my terminology. My objective is to get a longer cell life.

    In fact, many uses are a low to medium power draw, such as wireless mice, wall clock, MP3 players, etc. They are not as demanding as
    Quote Originally Posted by SilverFox
    then discharging it at 2.5 amps down to 0.8 volts.
    Now I realize this method was chosen for speed, so don't suggest you test other "slower" scenarios, fair enough. My question is if there is a way to extrapolate from your tests or some other trick to derive from your tests results for this other scenario?

    "Slow" (0.1C to 0.2C) charge rate and "low" power draw rate (max 0.3C)

    For me at least this scenario would represent the majority of uses, hence I am more interested in it. It is especially relevant to the multitude of electronic gadgetry that doesn't have electric motors or other moving parts.

    Again, not to diminish your work, it just doesn't represent most of my use scenarios. The tests seem to show that after 150-200 cycles the cells were degraded, unusable for most applications, compared to claimed 500-1000 cycles. I thought NiCd handles about 1000 cycles and NiMH handles about 300-500 cycles (might have read it at the battery university site). I wonder if the "slow/low" scenario would get much closer to the 500 figure.

    As an example from real-life slow/low scenario, I have solar lights in my driveway. Each has a pair of NiCd AAs and a LED light. Clearly it is a slow charge rate as solar panel is small. I assume it is a low power draw as LED is tiny compared to reular flashlight lamps. From the original set most of them have suffered from "accidents" (lawn mower and such). The 3 remaing lights still work very well. I think they are about 3 years old, which is 3 x 365 = 1000 cycles. In fact, they survived temperature range from -30C to +30C.

    Hence cells can last a very long time and even exceed specs.

    Again great work on your part and I am not attacking/criticizing it. Just wondering if there is a way to estimate slow/low scenario cycle life without spending yet more time/effort.

    thanks

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    Default Re: Cycle Testing Observations…

    Hello Bob,

    I believe most of the test data that suggests 300-500 cycles has been done with lower capacity cells. I need to do another round with 2000 mAh cells and see if they hold up better.

    I believe the only way to get the information you are looking for is to test using 0.1C charging and 0.3C discharging. Unfortunately, several hundred cycles would take a lot of time...

    I got about 5 years out of my NiCd cells in my solar yard lights. I don't think they were full cycling every time, but in the winter they never completely charged up. However, they were only 900 mAh cells. I replaced them with 1000 mAh cells and they are working fine.

    Tom
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    Most batteries don't die - they are tortured to near death, then murdered...

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    Default Re: Cycle Testing Observations…

    Silver thanks for taking the effort to do this and represent the data.

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    Default Re: Cycle Testing Observations…

    Update:

    I am doing a test on Titanium 2000 mAh cells. I am using the same chargers and will follow the same test procedure, however since I am seeing a similar drop in voltage I will be adding a "forming" charge every 25 cycles. This should give the "best" chance for the most cycles.

    Testing in progress...

    Tom
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    Most batteries don't die - they are tortured to near death, then murdered...

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    Default Re: Cycle Testing Observations…

    I just looked at this thread for the first time. Very interesting results. I would be interested in seeing if there is any improvement in cycle life using reflex (also known as burp) charging, and also if this charging method can revive the cells which have lost their capacity. Problem is I'm not aware of any commercial chargers which use reflex charging. Also, while the number of cycles you're getting seems low you're stressing the cells much harder than most normal usage. Still, the results are encouraging. Even with fast charging you get 100+ cycles before significant capacity is lost. In a situation where someone recharges their cells once a week that's two years of use. From a cost standpoint (compared to disposable cells) that comes to $0.03 per cell (assuming the Sanyos cost $3 each). That's still an order of magnitude cheaper than disposables.

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    Default Re: Cycle Testing Observations…

    Thankyou Silverfox for the hard work you are doing for CPF.

    Your threads is the first i read every day and in most cases the most interesting ones.

    Anders
    Last edited by Anders; 09-23-2006 at 01:32 PM.

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    Default Re: Cycle Testing Observations…

    Hi there,

    Just a note for some that were talking about partial charging their cells
    more often...

    A partial charge does not count as a full cycle. You can probably top off
    your cells many times before it equates to having used one full charge cycle.
    Take care,
    Al
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    Default Re: Cycle Testing Observations…

    Hello JTR,

    The ICE charger can do reflex charging, but it won't bring the cells back to life. I have tried several chargers (including the Schulze and ICE, and others) and several charge rates and have not been able to get the test cells to "recover."

    Tom
    Behind every Great man there's always a woman rolling her eyes...

    Most batteries don't die - they are tortured to near death, then murdered...

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