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Thread: Replace Ni-Cd BIOS battery with Ni-MH? Is that safe?

  1. #11

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    Thanks to everyone for your valuable feedback, ideas and thoughts. Really appreciated. Well i guess will order some Ni-MH then.

  2. #12

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    Quote Originally Posted by Chuck(G) View Post
    Well, I like Eneloops a lot, but I'm not sure how long they'd last with a steady, unsophisticated trickle charge.
    I've been using them for years in handheld transceivers that I rarely use. They stay plugged into their chargers intended for NiCd battery packs. When I do use one, it tends to be taken off the charger and intermittently used for a month, and then rotated to a different one.

    I don't have any data to say that they work as well as they did when they were new. But I've replaced standard NiMH and lithium packs that were the same age, in the same time frame.

    Batteries that last a long time go unnoticed. The battery in my wife's car died recently, and I was furious. I paid a lot of money for that Optima battery, not that long ago. Then my wife pointed out the tattered receipt which shows that I bought it twelve years ago.
    Be polite and I may let you live.

  3. #13

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    I'm a bit concerned about replacing NiCADs with NiMH batteries.

    They are a 'drop in replacement' when being used to power a device. My previous reading tells me that they are not a drop in replacement when being charged. So if you put them in laptop and the laptop charges the batteries, that could be problematic.

    I'm not an electrical engineer so I'm not about to start redesigning charging circuits in laptops. My approach would be to replace the cells, but do not attempt to charge them with the existing charging circuit.

  4. #14
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    Exactly, Mike. Primitive charging circuits found in old PC clock+SRAM are essentially constant-voltage affairs (take a look at any reference design from that era).

    Really, if it's a clock+SRAM type of application, use a couple or three AA-sized alkaline primary cells with a blocking diode and keep the bloody things off the PCB. Replace every 10 years or so. I've got several systems set up that way and have no regrets.

  5. #15

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    I tried to convince him but he then turned around and
    decided to go with Ni-MH. It seems to me that for the cost and hassle
    some large D alkalines would out last the fellow.
    Dwight

  6. #16

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    Well I don't think I'm the right guy to remove the correct resistor from such a miniature motherboard and i also don't paln on using the laptop very often - usually i get it out like once in a year, play a bit with it and that's it. I do like the idea of having some AA batteries and a diode as a replacemt, will sure try that in an old desktop one day, but these wouldn't fit in the Intertop as it really doesn't have much space in there.

  7. #17
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    Got enough room for a CR2032 or two?

  8. #18
    Join Date
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    Cincinnatus, Ohia
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    Try GOOGLING for the specific battery type with your location included.

    For just "3.6v 200mah nimh battery" GOOGLE gave me About 512 THOUSAND results (0.71 seconds)

  9. #19

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    I know, fiddling with arduino and clock modules, there are rechargeable
    button cells ( I think similar to the 2032 ). I just forget the number.
    Most don't realize when they buy these modules that you have to cut
    the jumper trace, especially if running at 5V, that the cell will go open
    in a short amount of time. These cells should normally last for 5 years
    on the typical drain.
    Some of the modules do come with the right cell but they don't tell
    you that they don't get charged when running at 3.3v.
    The switch/display modules have similar design errors.
    Dwight

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