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charging 9 volt batteries

Discussion in 'Electronic Repair' started by john d hamilton, Sep 2, 2008.

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  1. I have a few 9v Ni-MH batteries 200mAh.

    I have two chargers one with output at 9v of 10ma and the other a very old
    one that says output is 7.2v (even though its designed to take two 9v
    batteries) and whose output says it is 15ma x2.

    Which would be the best to use on the 9v Ni-MH and what would be roughly be
    the minimum charge time to ensure batteries are fully charged please?
    thanks for advice.
  2. VanguardLH

    VanguardLH Guest

    The one that is designed to recharged NiMH batteries. The charger needs
    to cease charging NiMH batteries when they reach full charge and then
    not charge thereafter (i.e., no trickle charge to top-off the battery).
    If a thermistor is not used to detect a full charge then a timer should
    be built into the recharger to ensure the charger turns off (to no
    longer continually try charging the battery).

    NiMH should be charged at a very low rate. It is unclear if 15mA x2
    means 15mA is used for each of 2 battery slots or if it gets split and
    7.5mA is used for each battery. You didn't indicate if the both
    chargers were expressly designed to recharge NiMH batteries or if they
    might be for rechaging NiCad batteries.
  3. GS

    GS Guest

    There are two types of rechargeables. 7.2 volts and 8.4 volts. You
    obviously can't charge a 8.4 with a 7.2 volt charger. Know your
    battery type. it should say on the battery what the actual voltage is.
    A 230 mahr battery would need 23 hours at 10 ma.
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