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  1. #1
    Senior Member Richard Cranium's Avatar
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    A "gimmick" or schedule to recharge NiMh regularly

    Ok, so I got a good light, I got my batteries, and chargers etc.

    Now, how to do I start a routine to know when I should recharge or otherwise keep batteries "ready to go" when I am not actually draining them very often through usage.

    What's the "shelf life" for a "AA" battery's charge?

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    Nimh suffer from quite rapid self discharge.

    Keeping them 'ready to go' is virtually impossible.

    If you want batteries that can be 'ready to go', buy Lithium Ion.

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  3. #3
    tad
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    Quote Originally Posted by Unknown Cyclist View Post
    Nimh suffer from quite rapid self discharge.

    Keeping them 'ready to go' is virtually impossible.

    If you want batteries that can be 'ready to go', buy Lithium Ion.

    a year or two ago, this was the right answer.
    but today - we have beauties referred to as low-self-discharge (LSD batteries).
    The best (and most popular) are sanyo eneloops. The white-topped duracells (commonly referred to as "duraloops" are allegedly rebadged eneloops). I've had good experience with the Rayovac hybrids as well.

    Point: All of these will hold a charge for months. Perfect for your needs, it sounds like.

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    yep sanyo eneloops are super - worth the extra cost

  5. #5
    Zoom zoom zoom zoom bonk znomit's Avatar
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    Normal NiMH drop 10% over the first day or two and then 1% per day.
    Monthly is probably a good way to remember.

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    Quote Originally Posted by tad View Post
    we have beauties referred to as low-self-discharge (LSD batteries).
    The best (and most popular) are sanyo eneloops. The white-topped duracells (commonly referred to as "duraloops" are allegedly rebadged eneloops).
    Fair point, I should have mention low self-discharge (NT) batteries.

    I would add that it's best to avoid cheap New Technology batteries - not all low self-discharge batteries are actually any good. I've tried a couple of brands that actually self-discharge faster than normal Nimh.

    When I bought a P7 torch I had to also buy 18650 batteries and a charger - the fact that I now have these batteries that don't self-discharge was an additional bonus and one that I hadn't considered before.

    Given the choice between Nimh and 18650s, I'll be using 18650s wherever possible.

    Unless there has been a recent increase in capacity, NT Nimh are lower capacity than standard Nimh so for me this is a choice of two evils.

    Do you choose the larger bucket that leaks faster or the smaller bucket that leaks more slowly ?

    Also there is cost and energy density, a single 18650 stores more energy than 3 x AA NT Nimh, it weighs less, takes up less room, has less self discharge and costs less to buy.

    I'm not attacking Nimh or NT Nimh - I have dozens of them - just making a few points clear that I've become aware of since my first semi-reluctant 18650 purchase.

    If I could have bought a P7 torch that ran on Nimh I probably would have bought one - now I've tried 18650s I'm aware that there's no comparison and that 18650s were the best choice.



    Back to the original question - no, a shedule won't really help - the best thing is to put some of your batteries on a slow charge a few hours before you want to use them.

    Keeping them in sets, labeling them and rotating them can all help.
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    If you have a good charger leave them in it until needed. Once in a while let the charger take them down to 1 volt and recharge them.

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    Senior Member Richard Cranium's Avatar
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    Part of the reason for my question was because I discovered "dead" batteries on a ride. They had been used for an hour, and should have had 50% of their charge left - but that was two weeks after charging.

    So bottom line, is to "top off" - or recharge batteries before you use. Assume batteries have lost at least 20% charge when left on shelf for a week or more.

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    yes, or get some eneloops - they can sit around for weeks without losing significant charge

    with regular nimhs you need to charge them every time right before use - with some devices, nimhs will not have adequate charge to operate device after sitting around only 2-3 days.

    test your own with a voltmeter - you'll be surprised how fast they drop just sitting on a countertop for a few days

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    Senior Member Ziemas's Avatar
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    Quote Originally Posted by Richard Cranium View Post
    Part of the reason for my question was because I discovered "dead" batteries on a ride. They had been used for an hour, and should have had 50% of their charge left - but that was two weeks after charging.

    So bottom line, is to "top off" - or recharge batteries before you use. Assume batteries have lost at least 20% charge when left on shelf for a week or more.
    It sounds like you have low quality batteries. Are the 2500 Energizers perhaps? They are famous for extremely fast self discharge. I did a test with some Sanyo and Powerex 2700 batteries and found that after two months they still had a greater capacity than 2000 Eneloops fresh of the charger. YMMV.

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    Senior Member Richard Cranium's Avatar
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    I did a test with some Sanyo and Powerex 2700 batteries and found that after two months they still had a greater capacity than 2000 Eneloops fresh of the charger. YMMV.
    If this is true, then it would seem that whatever the quality of the chemisty of a given run of a brand of battery would emphasize "charged shelf life."

    I wonder if there is a published review generated from a professional investigation of the "charged-shelf-life" character of different battery brands? It would seem the EMS and DOD specs would require some sort of "best practice" statement.

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    Senior Member Ziemas's Avatar
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    Quote Originally Posted by Richard Cranium View Post
    If this is true, then it would seem that whatever the quality of the chemisty of a given run of a brand of battery would emphasize "charged shelf life."

    I wonder if there is a published review generated from a professional investigation of the "charged-shelf-life" character of different battery brands? It would seem the EMS and DOD specs would require some sort of "best practice" statement.
    Go check out the batteries section at CPF for all your needs. There is a wealth of info there, much of it academic....

    http://www.candlepowerforums.com/vb/...isplay.php?f=9

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    Quote Originally Posted by Unknown Cyclist View Post
    Nimh suffer from quite rapid self discharge.

    Keeping them 'ready to go' is virtually impossible.

    If you want batteries that can be 'ready to go', buy Lithium Ion.

    That's not even true. NiMH have a self discharge of 30% per month or about 1% per day. If you can regularly get by on half the batteries charge then keeping them ready to go means charging them about once every 6 weeks or after you make use of them.

    I doubt that the low self discharge cells are good enough to work well with most lights. The off the shelf NiMH's (Energizer) I have won't even work in my underpowered cateye if it's below 30 degrees (they discharge in about 10 minutes). But the high discharge NiMH's that came special with my stella 120 will run for almost 2 hours when it's below zero.

    You can also store NiMH's in the freezer to bring the self discharge down to almost nothing. Good cells will run even when they've been frozen at this temperature. Other cells will need to defrost first. This is pretty inconvenient for me, so I just try to recharge my battery packs about once a month. If I'm going to go on a long ride that will need them I make it a point to recharge them the night before.

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    Senior Member Ziemas's Avatar
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    Quote Originally Posted by crhilton View Post
    That's not even true. NiMH have a self discharge of 30% per month or about 1% per day. If you can regularly get by on half the batteries charge then keeping them ready to go means charging them about once every 6 weeks or after you make use of them.
    I've found that the rate of self discharge is far below 30% a month for quality batteries. Hell, I'm using regular Mi-MH batteries in my radio and I charged them about four months ago.....

  15. #15
    Senior Member Richard Cranium's Avatar
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    You can also store NiMH's in the freezer to bring the self discharge down to almost nothing
    That's an interesting comment. And I can appreciate the apparent logic that supports the idea that the chemical "state" or status of the battery would slow and therefore retain whatever condition it was in at time of freezing. Of course this begs yet another possible premise, that if indeed you can freeze batteries to successfully retain a particular chemical status - then what is the outcome for the batteries to cycle through their intended chemical changes necessitated during load.

    In other words - repeatedly preserving "shelf life" status could interfere with or damage the batteries to completely [de]ionize. Ok, enough into geekdom -but I appreciate the thoughts.

    Here's the situation, if I have a cheap Energizer trickle charger, and a slightly better Radio Shack quick charger with a "stop charging" sensing circuit, which charger is better to "re-top off" batteries that have sat around for a week or more - but have never been discharged by use?

    I understand you never really want to top off batteries that are already charged...... which charger provides the safer way to maintain my 16 battery collection?

  16. #16
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    NiMhs fast shelf discharge? Not compared with NiCads that had a shelf life of 3 months; NiMhs will last at least 9 months. I tried for curiosity sakes and ran a fully charged NiMh 900mh AA bat in a wall clock at the house and it ran the clock for a 11 months, did the same with a Nicad some years ago and the same clock ran for about 2 months. This NiMh I used in the clock was 5 years old and had been used numerious times in other stuff.

    The freeze can actually damage batteries, your better off putting them in the frige.

    Also according to Voltman, NiMh's last longer if you charge them up after every use regardless of the state of discharge.

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    Quote Originally Posted by Richard Cranium View Post
    That's an interesting comment. And I can appreciate the apparent logic that supports the idea that the chemical "state" or status of the battery would slow and therefore retain whatever condition it was in at time of freezing. Of course this begs yet another possible premise, that if indeed you can freeze batteries to successfully retain a particular chemical status - then what is the outcome for the batteries to cycle through their intended chemical changes necessitated during load.

    In other words - repeatedly preserving "shelf life" status could interfere with or damage the batteries to completely [de]ionize. Ok, enough into geekdom -but I appreciate the thoughts.

    Here's the situation, if I have a cheap Energizer trickle charger, and a slightly better Radio Shack quick charger with a "stop charging" sensing circuit, which charger is better to "re-top off" batteries that have sat around for a week or more - but have never been discharged by use?

    I understand you never really want to top off batteries that are already charged...... which charger provides the safer way to maintain my 16 battery collection?

    What kind of NiMH's are they, old fashioned or the newer low self discharge? I run low self discharge (sanyo eneloop) in everything now and top them off after each use or every 6 months. Then about once a year a run ana anlyze cycle to see where they are at, it replaces one of the 6 month top off cycles. Anything non eneloop now I'm just using in kids toys and those get charged whenever the toy slows down or dies, they are all older, some 10 years now so I don't care if they get any kind of maintenance or not. Good quality NiMH's need very little maintenance, just just top off and check mine so I know they are always ready.

  18. #18
    Senior Member Richard Cranium's Avatar
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    Also according to Voltman, NiMh's last longer if you charge them up after every use regardless of the state of discharge.
    Thanks, I'm about all geeked out for charging talk.

    Heat and cold are bad things, charge batteries whenever they discharged, re-charge before use if the batteries have not been charged for while.

  19. #19
    Senior Member Road Fan's Avatar
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    Richard, the rate of chemical reactions slows with temperature by a factor of two for every 10 degrees C of temperature drop. If the cell loses 50% in say a month, by storing it at 15 C (room temp is around 25 C) should significantly slow the self-discharge. I wouldn't freeze them unless there was a good study that says nothing bad is going to happen. The effects of a phase change might not be easy to predict, and might not be reversible. Storage cells have complex chemistry.

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    Seems like it would just be easier to use low self discharge rather than put them in thew freezer.

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