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Thread: How or can you determine if it is safe/wise to you rechargeable batteries in a light?

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    Flashaholic TimeOnTarget's Avatar
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    Question How or can you determine if it is safe/wise to you rechargeable batteries in a light?

    How do you determine if it is safe to use a rechargeable battery in a light that is not advertised as being able to use rechargeable batteries?

    I have an ElZetta Bravo that I use a 16650. ElZetta does not recommend it due to reliability issues, but they say that it is safe to do.

    Specifically, I have a Streamlight TLR-1s weapon light that uses 2 123A batteries. I tried it with OLight CR123 batteries and it worked just fine.

    Your thoughts are much appreciated.

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    Flashaholic* Timothybil's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Your options are somewhat limited here. You could try using a 16650 cell, but you would be providing 3.7v instead of the 6v of the two 123A cells, which may not be enough. The only other real option would be two 16340 FeSO4 cells, since their 3.2v cell voltage would be providing 6.4v instead of the 6v of the 123A cells. That may be close enough, but the only test is a potentially destructive one. Streamlight is notorious for not OKing the use of rechargeable 123A/16340 cells.
    Basically, any time one is considering using rechargeables instead of primary cells, one has to see how closely the voltages match. Results of an overvoltage situation can range from immediately letting the magic blue smoke out, to rapid degradation of the driver electronics, to premature aging of the driver circuitry/LED, to no apparent damage. If we are talking about an incandescent light, any voltage mismatch will almost guarantee instaflashing the bulb.

    There are always going to be those who will tell you that they have done such and such a substitution without any problems, so far. What it boils down to is how willing are you to risk your light to gain the advantages of using rechargeable cells.
    Remember, Two is One, and One is None!.

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    Flashaholic TimeOnTarget's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Thanks for the response. That makes sense to me.

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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Your Streamlight may have a buck circuit that can handle 2X RCR123's. If the light output is the same with 2X RCR'123's as with two primary CR123's, then it has a buck circuit, and it will not hurt your light.

    Bill

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    Flashaholic TimeOnTarget's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Quote Originally Posted by Bullzeyebill View Post
    Your Streamlight may have a buck circuit that can handle 2X RCR123's. If the light output is the same with 2X RCR'123's as with two primary CR123's, then it has a buck circuit, and it will not hurt your light.

    Bill
    Are you saying to just visually judge if they appear to have the same output?

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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Find your darkest room, without windows, and shine. the light on the ceiling. You should notice a difference. Better way is to check current at the tailcap with a DMM. If the current reading is lower using RCR123's, then you have buck circuit, which will be safe.

    Bill

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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Quote Originally Posted by Bullzeyebill View Post
    Your Streamlight may have a buck circuit that can handle 2X RCR123's. If the light output is the same with 2X RCR'123's as with two primary CR123's, then it has a buck circuit, and it will not hurt your light.

    Bill
    Great info, thanks. I did not know that.
    It is better to buy a beautiful, expensive, custom flashlight than to curse the darkness.

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    Flashaholic TimeOnTarget's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Quote Originally Posted by Bullzeyebill View Post
    Find your darkest room, without windows, and shine. the light on the ceiling. You should notice a difference. Better way is to check current at the tailcap with a DMM. If the current reading is lower using RCR123's, then you have buck circuit, which will be safe.

    Bill
    I performed the visual check, and I could not notice a difference. I have a multi meter, but I don't know exactly how to test this tail cap. The light is a TLR-1s

    Thanks for your input.

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    Flashaholic* DIWdiver's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    I think Timothybil meant to suggest a LiFeP04 cell, not FeS04. That chemistry would be the safest choice for rechargeable cells, as it's closest to the original voltage spec. It's also safest from a smoke and fire perspective, but it does sacrifice a fair bit of capacity. Also, they are available in 123 size (I found 17335s). Right off charge, these can produce 3.5V per cell, though that drops rapidly to 3.3 or below.

    Why do you guys all say that if it's regulated, it's buck? There are lights using linear regulation, especially with the AMC7135 and similar parts. And note, the '7135 (at least in some incarnations) has a max input voltage of 6V. The extra 0.5 - 1 volt is unlikely to be a problem, but not impossible.

    I'll admit that a light running on 6V and linear regulation would not be very efficient, and a modern, quality light is unlikely to use this configuration. I think you are most likely to see it in older, cheaper, and space-constrained lights. But can anyone say SL didn't do this?

    Bullzeyebill has the best idea. If the current is lower when the voltage is higher, that's definitely a buck circuit.

    The definitive answer though, (short of getting it from the manufacturer), would be to get a look at the parts on the driver board. With that it's likely we can tell beyond any doubt.

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    Flashaholic TimeOnTarget's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    Well, I must admit that I a still a nooby, and some of this is going over my head. There are so many choices of batteries and there always seems to be lively debate about it all.

    I am beginning to think that for this specific application, I should just use primaries and stop worrying about it. It is not like I go through a lot of batteries in my weapon lights anyway.

  11. #11
    Flashaholic* Timothybil's Avatar
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    Default Re: How or can you determine if it is safe/wise to you rechargeable batteries in a li

    You are right, I meant LiFePO4. Don't know where the other one came from.
    Remember, Two is One, and One is None!.

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