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Thread: Storing LSD NiMH D cells fully charged

  1. #1

    Default Storing LSD NiMH D cells fully charged

    Hi all, a little background then a question:

    The need: I live in Florida in an area prone to extended power outages (in fact, I just recently got power back after being down a week after Irma). I also go camping once or twice a year. I have a bunch of handhelds that run on 18650's, but lanterns and fans are also a necessity and they run on D's. I have Siege lanterns and o2cool 10" fans - the sieges take 3 D's each and the fans take 6 D's each (I would love to consolidate to all 18650, and CL30R's would be an option for lanterns, but there are no decent options for 18650 fans, so I'm stuck with 6 D cell fans or jobsite fans with horrifically expensive proprietary battery packs for now). So, I need to keep a bunch of D cells around, often times for 6 months or a year between uses, but when I need them I might run them and recharge them several times over for a week or two straight.

    The equipment: I have an ample supply of rechargeable D cell batteries. Some are Maha (Imedion) 9500, some are Tenergy 8000, and all are LSD (I never mix the two in the same device). For chargers I have a Maha 808m and a Xtar VP4 Plus Dragon. I top everything off when hurricanes approach, and I have an electric car that I use as a 90 kwh power bank when the power goes out, so recharging batteries is not an issue. However, sometimes the need arises without warning.

    The issue: Storage! I very much prefer storing these batteries charged. The LSD batteries advertise that they "retain 85% of their charge after a year in storage" and that they can "be stored for 12-24 months with a high capacity percentage left." Thus, I'm assuming storing them fully charged is an option. My chargers have a "battery conditioning" mode. Currently I'm just topping them off every July and January if they haven't been used in the previous six months.

    The question(s): On these LSD batteries, is storing them fully charged a reasonable option? Also, is there some recommended procedure/preventative maintenance that I should be performing periodically (monthly? semi-annually? annually?) to keep the cells as healthy as I can for as long as I can? If anyone has any insight on this issue it would be greatly appreciated!

  2. #2
    Flashaholic* ChrisGarrett's Avatar
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    Default Re: Storing LSD NiMH D cells fully charged

    I store my many AA/AAA LSD batteries fully charged. I would do the same with my Ds, if and when I get some. They'll self discharge a little, so they won't be at 100% for too long.

    For my extra li-ion cells, I bump them down to 3.60v-3.70v and stick them in the fridge. For the others in rotation, I keep them charged, unless I won't be using them for a few months.

    Until hurricane season is done, they're staying charged up, regardless of usage. Same with the gas in my dinky HF generator. Another 4-6 weeks isn't going to matter too much, IMO.

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    Default Re: Storing LSD NiMH D cells fully charged

    Hello Frottage,

    Welcome to CPF.

    The down side to storing LSD cells fully charged is that they may not last as long. Keep in mind that "as long" has yet to be totally defined.

    I purchased some Eneloop cells when they first came out and after roughly 7 years sitting fully charged in not frequently used applications they died. With emergency equipment I would suggest replacing the cells say every 5 years.

    It should be possible to extend that life by storing the cells at lower states of charge, but I don't believe that study has been done yet so I don't know if the gains would be worth the effort.

    Tom
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    Default Re: Storing LSD NiMH D cells fully charged

    Quote Originally Posted by SilverFox View Post
    Hello Frottage,

    Welcome to CPF.

    The down side to storing LSD cells fully charged is that they may not last as long. Keep in mind that "as long" has yet to be totally defined.
    On the other hand, I donít think storing at full charge is NEARLY as detrimental to NiMH as it is to Li-Ion.

  5. #5

    Default Re: Storing LSD NiMH D cells fully charged

    Thanks guys, exactly the info I was looking for

  6. #6
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    Default Re: Storing LSD NiMH D cells fully charged

    Since fridge was mentioned; just keep in mind that the fridge is a relatively humid or even wet environment, so moisture control is required if you go that route.

    Personally I store NiMHs fully charged, but check them every 6-18 months or so, and LiIons charged to about 3.92V, check every 3-6 months, neither of them in the fridge.

    I live in Norway though, and inside temperatures are rarely above 25C.

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    Default Re: Storing LSD NiMH D cells fully charged

    Welcome to the forum.

    Hilarious nickname, BTW. :-)
    It is better to buy a beautiful, expensive, custom flashlight than to curse the darkness.

  8. #8
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    Default Re: Storing LSD NiMH D cells fully charged

    Quote Originally Posted by SilverFox View Post
    The down side to storing LSD cells fully charged is that they may not last as long. Keep in mind that "as long" has yet to be totally defined.
    You'll love my testing in this area described a bit later down!

    Aye - there's the rub: LSD cells may retain their charge for a long time, BUT the performance of those cells with any reasonable load may be an issue a few years down the line if all you do is a top-off. You may not notice any problem the first year or two, but without any decent exercise, like muscles, they atrophy.

    I purchased some Eneloop cells when they first came out and after roughly 7 years sitting fully charged in not frequently used applications they died. With emergency equipment I would suggest replacing the cells say every 5 years.
    I would say this is reasonable if one doesn't exercise the cells - and that doesn't mean just a top off, or even a gentle break-in done yearly or so. We are babying these cells to death after the first year or two.

    Here's the test:

    Battery: 6 year-old Gen 1 AA Eneloop. Charged with Maha MH-C9000 or other high quality chargers with an appropriate rate to detect the minor dv/dt or other backup trigger.

    Load: Aviation clock single cell. Would run for about a year until it slowed down 5 minutes behind the real time. Just topped it off in the '9000. After about 3 years, the runtime between top offs shortened to 6 months, then finally to an annoying 3 months or so.

    Measure: Discharged at the 0.2C rate and got about 1680ma capacity from it on the '9000. Internal resistance per the '9000 is at 1.68 (not voltage, but initial IR measurement - not bad!)

    Voltage Depression! Despite having plenty of capacity left, the voltage drop on discharge was very interesting after an initial top off. Voltage dropped rapidly to just over 1.1v, where it flatlined very near 1.1v while discharging for a little over two hours and get this - it took about hour to discharge from 1v down to 0.9v where it finally stopped - and that's with the discharge rate at 500mah.

    I believe that the lack of any decent exercise contributed greatly to this aging effect. My own experience with other regular nimh cell packs has shown that this aging, if caught soon enough, can be greatly reduced by not pampering the cells. Cells that have the voltage depression from chemical inactivity can be brought back somewhat by using at *least* a 0.5C discharge, followed by a normal 0.5 to 1C recharge.

    In other words, my testing showed that pampering the cells can do just as much harm as overcharging them - but you don't see this in the short run.

    I no longer just let my LSD cells sit in the fridge forever with occasional top-offs. On a regular basis, because they aren't seeing any use, after coming to room temp for a few hours, I put a health (but not abusive) cycle or two on them before storing again. Believe it or not, to save some time, I'll even use the older Maha MH-C401FS "reflex" charger for this sometimes.

    In the other op's case, using 8000mah LSD Tenergy's, which I also have, that means using a hobby-charger with about a 4A discharge (0.5C) on a regular 6 month to yearly basis if one is not going to be actively using the cells on a regular basis. It might be more convenient to just buy new cells every few years.

    It took a few years of work with these and Motorola nimh battery sets to see what the chemical degradation from just sitting around fully charged will do - even if they are not being trickled to death. Lack of chemical activity from a decent load once in awhile really hurts.

    In fact, it was your eariler descriptions of how to keep cells "vibrant" that got me to do this years-long test. Sure enough, the cells go "dormant", even if they seem to keep their voltage and capacity up with a minor load like a simple clock - any decent load thereafter just depresses the voltage like a rock, flatlining to a voltage level that much of my gear doesn't like.

    Hope my wacky 6 year long experiment helps.
    Last edited by IonicBond; 10-08-2017 at 01:03 AM.

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    Default Re: Storing LSD NiMH D cells fully charged

    Hello IonicBond,

    Interesting observations...

    My original thought was to store LSD cells at a low state of charge and then to subject them to a 1C charge/discharge about once a month. This may actually be not too far off from how to keep them healthy.

    I too have noticed the voltage depression and also noticed the level off at 1.1 volts. This was not too far off from the 1.2 volts I expect so I didn't pay much attention to it.

    Thank you for your efforts. I guess the plan is to use these cells to get the most from them. Storing at full charge doesn't seem to bring the best performance.

    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: Storing LSD NiMH D cells fully charged

    That all suddenly explains why my Nikon D300 keeps complaining about 'empty' AA's in the grip, even though they are 60% full.

  11. #11

    Default Re: Storing LSD NiMH D cells fully charged

    OK, this is a bit surprising. Actually, it was shown in previous tests that Eneloops, while maintaining their capacity, develop a higher internal resistance when left untouched for a longer time, leading to voltage depression depending on the load. The same thing is triggered in the longer run by not discharging them completely, which is somewhat comparable to the memory effect found on NiCd batteries, only that it takes several cycles to build up. I found that this also occured on my wireless phone where the batteries were basically trickled to death (possibly at a pretty high rate because they got pretty hot) with occasional, not very deep discharges by doing calls. In this case, however, I only managed to bring them back to usable once, on the second time the high internal resistance was permanent.

    Now I try to make sense of this and squeeze it into a formula. So for me the following points would be interesting to know:
    - When the runtime decreased to 6 months, was this for only one additional cycle and then the next was 3 months? Or did it remain at 6 months for multiple cycles?
    - Do you know what the cutoff voltage of your clock is, i.e. the voltage at which it starts to slow down? Could be that a high cutoff voltage led to this by not discharging the batteries completely.
    - How well did you manage to bring back the cells, and how many cycles did it take to do so?

    It's interesting that the high internal resistance seems to build up even if the batteries get recharged once a year, not only by putting them through many cycles or letting them sit for many years without a recharge. Maybe it's actually dependent on the time the batteries spend without a complete discharge... but I'm not sure about this.

    About the economics of it... yes, it might be more convenient to replace the batteries after a few years, but more so for the cheaper AA's and AAA's than for the more expensive D cells. Just for the record, I'm still using the same set of LSD D NiMH's (Conrad energy) in my boombox which I bought in summer 2010, over 7 years ago now. They go through a cycle every 2-3 weeks, but only at very moderate rates (charge is about 500 mA, discharge at 120-200 mA mostly with only occasional bursts of 2-5 A in a ride-on toy), and I take care not running them down completely. However, these are not Eneloops, and I've also seen in some self-discharge tests that in other models of LSD cells, the IR raise may actually be less pronounced than in Eneloops.

    But if you have to replace the batteries after a few years, it might actually be better to use Alkalines for devices that take a recharge that infrequently. Or you may ask yourself if you really need Eneloops for that job or if cheaper no-name LSD cells would do as well. That's what I want to find out with my calculation, so I'd appreciate any additional input on this matter.

  12. #12
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    Default Re: Storing LSD NiMH D cells fully charged

    Well, that's the funny thing - the 9000's IR reading for this 6 year old cell is sitting at 1.68 (not volts, but ir - the very first value shown and shown only once). Not bad! Here's the breakdown:

    1.60v = new good cell
    1.80v = middle aged
    2.00 = old cell
    >2.1v = rejected by 9000

    Ballpark. So something other than IR is going on. Is my minuscule clock-load / top-off enough to keep the IR reasonable, yet underneath the chemicals are aging so that voltage depression still occurs?

    I think we just have to regard nimh batteries like muscles - use 'em or lose 'em. The bodybuilding analogy would be like doing a single 100 lb bench-press once a month won't keep you strong. Neither will curling a handful of fishing-weights every day.

    What I can say is that doing the typical 0.2C discharge for capacity measuring is just that - an overall capacity measurement that the industry uses as a standard. But to me, it is NOT a large enough discharge current to keep the chemicals vibrant. 0.5C from a chemical maintenance standpoint would be my minimum.

    By not hitting the cells hard enough, I think they go dormant with superficial "skin-depth" or surface charges / weak discharge. Maybe not noticeable in the first year or two. After that, the pampering becomes detrimental.

    Now that the 6 year long clock-test is over, I am using the same cell, but putting it through an earlier Maha MH-C401FS reflex charger. (negative pulse, burp, yadda yadda). My intent is not so much to speed the charge process, but hoping that the negative pulse will give the cell the discharge exercise it needed for so long without having to just run the cycles down unnecessarily with a more standard charger. Using the 1000mah / fast mode in the hopes that this does actually use a negative or reflex pulse. Following instruction to the letter - plug in charger first, THEN insert batteries.

    (I've seen and read all the marketing pros and cons about this, so we don't need to go there and rehash that. I'll just say it works for me, especially with older / aging batteries. New ones - you may not see any benefit up front if you are using them regularly right from the start. It has brought many pampered - but not abused or trash batteries - back in line for me. YMMV. Wrong forum, but we're also talking about the Advancetec chargers for commercial radio packs....)

    So we'll see. Hopefully I'll get a result lasting longer than 3 months on the clock.!
    Last edited by IonicBond; 10-10-2017 at 06:46 PM.

  13. #13

    Default Re: Storing LSD NiMH D cells fully charged

    I have a theory or two what could happen here:

    The internal resistance of a cell is not constant, rather there seems to be a short-time and a long-time value. The short-time value is the value by which the voltage drops immediately on applying the load, and by which it goes back up immediately after removing the load. If the internal resistance is measured at "1000 Hz" or something like this, it probably refers to that value.

    Then there's a longer-time value which comes into play if the load persists for a longer time. You can't even talk about a constant resistance there since this voltage drop isn't quite proportional to the load... even at very small loads like a clock it might be quite measurable. The voltage drop might exceed the short-time drop by many times in some cases. For instance, I once tested Alkalines in a portable cassette player. There was an initial voltage drop on turning it on, but over the next minutes, the voltage drop increased to nearly 3 times its initial value.

    The difference between those is the ability of the cell to deliver a burst of power vs. its ability to deliver a constant stream of power. If the chemicals have dried out, this stream might be hampered because the power, although it is stored, isn't able to run to the contacts quickly enough anymore... at least that's my theory behind it. So your cell might still be able to deliver a short burst of power, because it has accumulated some kind of surface charge, but shows a dramatic voltage sag if the current stays on.

    I've experienced something similar to this with sulphated Lead Acid batteries in an electric scooter, which gave quite good performance over the first 1-2 minutes after charging, but then the performance fell off a cliff (especially if you went out in the cold).

    Another thing is that at least the long-time voltage drop / voltage rise aren't really related to each other. The voltage your charger displays is the voltage on applying a current that goes into the battery, not out of it. Now I think it's plausible that if the battery gets hit with a load, it has trouble delivering it for a long time, but if it gets hit with a charge, it has no trouble sucking up the fresh electrons, hence the "good" reading. At least from lead-acid batteries, I know that the voltage falls off a cliff if you try to put a load on a nearly depleted battery, but when recharging it in that state, the voltage won't go up nearly as much. On the other side, the voltage will go up very much when charging a nearly full battery (as it will with Ni-Cd, Ni-Mh and Li-Ion as well), while it will be relatively stable when putting a load on a battery in that state.

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    Default Re: Storing LSD NiMH D cells fully charged

    I know that it's best not to store rechargeable batteries fully charged for long time. Still I find it a bit complicated to separate batteries I will soon use from those I will not.
    Consequently as well my NiMh and Li-ion cells are always fully charged...
    And if I want to not store them fully charged I would like the charger had the feature to charge them only to that optimal level for long time storage. Is there charger with this feature?
    Last edited by Swedpat; 10-14-2017 at 06:27 PM.

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    Default Re: Storing LSD NiMH D cells fully charged

    Quote Originally Posted by Swedpat View Post
    And if I want to not store them fully charged I would like the charger had the feature to charge them only to that optimal level for long time storage. Is there charger with this feature?
    The SkyRc MC3000 is great for this. I use mine all the time to charge LiIons to 3.92V whenever I put them away on a shelf for a while.

    Any lab power supply could be used for this as well btw, by setting voltage and current limits.

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    Default Re: Storing LSD NiMH D cells fully charged

    Quote Originally Posted by terjee View Post
    The SkyRc MC3000 is great for this. I use mine all the time to charge LiIons to 3.92V whenever I put them away on a shelf for a while.

    Any lab power supply could be used for this as well btw, by setting voltage and current limits.

    Thanks for tip! I read at THIS review that it's a good but advanced charger, not for everyone. I have still to learn the features of my new XTAR Dragon charger...

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    Default Re: Storing LSD NiMH D cells fully charged

    Quote Originally Posted by Swedpat View Post
    Thanks for tip! I read at THIS review that it's a good but advanced charger, not for everyone. I have still to learn the features of my new XTAR Dragon charger...
    What distinguishes an advanced user from a noice, isnít as much what you know, as the problems or tasks you identify as a thing to do. Identifying the want to charge to a specific voltage puts you well outside the noice class, and the rest is simply a matter of reading the manual. :-)

    Almost nobody *needs* the MC3000, but if you find the price okay, it wouldnít be an unreasonable purchase Iíd say.

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