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Can I substitute a NiMH battery for NiCd in a cordless phone?

Discussion in 'Misc Electronics' started by [email protected], Apr 17, 2005.

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  1. Guest

    I recently bought a cordless phone, which came with a NiCd battery. In the
    manual it says:

    "To reduce the risk of fire, use only 3.6V 850mAh Nickel
    Cadmium (Ni-Cad) cordless telephone replacement
    battery pack."

    I've heard about the dreaded "memory effect" with NiCd batteries, so I'm
    interested in replacing it with a NiMH one. Someone who is selling a 3.6V
    1000mAH NiMH battery on Ebay claims it works with my phone, but will it really
    be safe? Wouldn't want to install a NiMH battery and have the house burn
    down.
     
  2. CWatters

    CWatters Guest

    I thought most phones came with NiMH cells these days for environmental
    reasons.
    The memory effect is much misunderstood and isn't the most likely cause of
    cells failing to perform as expected.

    Memory effect was first noticed in early satellite batteries that were
    subject to many IDENTICAL charge and discharge cycles as the satellites
    orbited the earth. When the cells were asked to discharge a bit more than
    usual the voltage fell more than expected. This happened at the point at
    which it would normally have been recharged.

    In a phone the most likely cause of failure is long term overcharge. Once
    the battery is fully charged most phone chargers switch over to a
    maintenance charge program. This is designed to keep the cells topped up
    because all cells "self discharge". Problems occur if the chargers over
    estimate the self discharge rate. In fact dumb chargers have to use a
    slightly high maintenance charge rate to allow for the variation between
    different cell batches, temperature effects and aging. NiMH have a higher
    self-discharge rate but not everyone sees this. They are also less tollerant
    to long term overcharge.

    Personally I always prefer to buy products that use loose AA size cells
    rather than an assembled battery pack. That way if the manufacture has gone
    bust you can still replace the battery.
     
  3. JM

    JM Guest

    quoting:
    Ready made NiMh cordless batteries have cells that are spec'd for this kind
    of service. It is in my experience that the NiCad packs are not
    generally spec'd in the same way, so actually the NiMh packs are far better.
     
  4. L

    L Guest

    It says to charge them for 24h ...

    The Panasonic replacement battery costs as much as a new phone .. so i
    said "my ass" and found this cheap NiMH pack in a supply store for $4
    :)

    Matt
     
  5. L

    L Guest

    My NiCd's suffer from all known battery abuse :(


    Thanks all for the replies. I will go ahead and install the NiMH's :)

    Matt
     
  6. Guest

    Interesting, both you and CWatters mention that NiCd batteries handle
    overcharging better than NiMH. Maybe I'll stick with the NiCd battery.
    12 hours.
    Good to know.

    Thanks, everyone.
     
  7. Guest

    Interesting, the NiCd battery that *comes with* the phone isn't designed to
    handle the phone's charger?
    I will take this into consideration, thanks. :)
     
  8. PeteS

    PeteS Guest

    The problem lies in the charging. NiMh and Nicads are similar, but not
    the same, and NiMh in particular has unfortunate side effects if not
    controlled properly during charge (like smoking).

    Look at websites devoted to battery chargers (TI, Maxim, Linear Tech)
    and you'll find each has its own charge techniques. Having implemented
    chargers for both those (and others, such as Li-Poly and Li+), I can
    assure you there are differences and you have to be really careful.

    Cheers

    PeteS
     
  9. Ted Edwards

    Ted Edwards Guest

    I also recently bought a cordless phone that came with a shrink erapped
    3-AA cell NiCd battery. The phone would last for about 3 days of zero
    to minimal use before the battery went dead. I picked up an identical
    shaperd 3-AA NiMH pack at Walmart and substituted that.

    Now, the charger was designed to charge the 650mah NiCd pack at about
    C/10 so the charge rate for the 1300mah NiMH pack is only C/20 and is
    most unlikely to harm it. 1300mah is pretty low for NiMH AA's but the
    phone now runs for well over a week so we shall see.

    Ted
     
  10. CWatters

    CWatters Guest

    I have a six year old DECT system and this appears to switch rates.
    Initially it charges at a constant rate then presumably when the cells ar
    full it switches on and off roughly every 15-20 mins. The NiCad batteries
    last about 18 months then we notice they either get hotter and hotter while
    on charge or their capacity seems degraded.
     
  11. JM

    JM Guest

    quoting:

    Yes, that's generally what I see in the original NiCad batteries that come
    with phones AND replacement NiCad's.
     
  12. JM

    JM Guest

    quoting:

    But remember the cells used to make the NiMh pack are spec'd for continuous
    slow charge so even slightly higher charge rates won't harm the battery.

    These cells have the capability to recycle excess gassing back to the
    electrolyte (up to a cirtain point), rather than overcharge damage the
    battery. The trade you get with these cells is lower capacity.
     
  13. L

    L Guest

    I have been charging for 18 hours now and the phone is as dead as can
    be .. original battery was 3.6V 600mAh new one is 3.6V 300mAh ...

    Looks like that battery was DOA :(

    Matt
     
  14. it is more likely that the charging circuit is haywire.
    --
    ----------------------------------------------------------------------
    Mark W. Lund, PhD ** Battery Chargers
    CEO ** Bulk Cells and Custom Battery Packs
    PowerStream Technology ** Custom Power Supplies
    140 S. Mountainway Drive ** DC/DC Converters
    Orem Utah 84058 ** Custom UPS
    http://www.PowerStream.com ** Engineering, manufacturing, consulting
     
  15. L

    L Guest

    it worked (sort of) withthe NiCd'a do you think the NiMh battery killed
    it?

    Matt
     
  16. CWatters

    CWatters Guest

    No not unless the battery was faulty.
     
  17. I can't imagine that it could have, there is already a current limit,
    so even if the cell was shorted it probably wouldn't have damaged the
    charger.

    The way to tell, of course, is to measure the current while the battery
    is plugged in, but measuring the voltage when the battery is not
    connected should also tell you if it is working.

    If you don't have a voltmeter, get one. They are dirt cheap if you
    get one at Harbor Frieght, etc., and are an essential part of any
    man's toolbox.

    Best regards
    mark
    --
    ----------------------------------------------------------------------
    Mark W. Lund, PhD ** Battery Chargers
    CEO ** Bulk Cells and Custom Battery Packs
    PowerStream Technology ** Custom Power Supplies
    140 S. Mountainway Drive ** DC/DC Converters
    Orem Utah 84058 ** Custom UPS
    http://www.PowerStream.com ** Engineering, manufacturing, consulting
     
  18. JM

    JM Guest

    quoting:

    300mah, I think that's a typo. A NiMh pack made of the same physical size
    cells and having enhanced ability to be continuously slow charged without
    overcharging, this battery should be on the order of about 1300mah. If it's
    not working, do as another poster said; check the charger. There is also the
    possibility you received a defective battery with one shorted cell, bad
    joint, etc. Yes, it happens.
     
  19. Guest

    Alright, I'm definitely sticking with the NiCd. ;-)
     
  20. Dan_Musicant

    Dan_Musicant Guest

    On Sun, 17 Apr 2005 00:11:54 -0400, wrote:

    :I recently bought a cordless phone, which came with a NiCd battery. In the
    :manual it says:
    :
    :"To reduce the risk of fire, use only 3.6V 850mAh Nickel
    :Cadmium (Ni-Cad) cordless telephone replacement
    :battery pack."
    :
    :I've heard about the dreaded "memory effect" with NiCd batteries, so I'm
    :interested in replacing it with a NiMH one. Someone who is selling a 3.6V
    :1000mAH NiMH battery on Ebay claims it works with my phone, but will it really
    :be safe? Wouldn't want to install a NiMH battery and have the house burn
    :down.
    My oldest cordless phone is still going strong, and I feel strongly that
    it has NiCads, although I'm not certain. It must be around 7-8 years old
    or more. I always leave the thing charging.

    My other cell phones have been a different story. I have a Panasonic,
    that replaced (by RMA) a previous version of the same phone, and they
    have NiMH's. Both of these phone's manuals suggest not leaving the packs
    charging for maximum battery life, which is certainly a PITA. It's much
    easier to just leave it charging, since the base has to be plugged in
    regardless for the phone to work. However, in deference to that
    admonition I've not kept it charging but the first battery pack died in
    less than a year in any case. The newer one is still alive after maybe
    1.5 years, but I wonder about playing this game with it. NiMH's lose
    their charge faster than NiCads, so I find I have to put it back on the
    charger after 3-4 days or so and then guess when it's fully charged - I
    have to look at the LCD and see if the indicator suggests a full charge,
    not a game I enjoy.

    I'd seriously suggest just using the NiCads in this phone of yours and
    if and when they die, then think about replacing them, not sooner.
     
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