Any NIMH battery experts? I have a 9v NIMH

Discussion in 'General Electronics Chat' started by doug08, Sep 25, 2011.

  1. doug08

    Thread Starter Member

    Jan 30, 2011
    that is a 300mah battery. I have several of them. I tried this test with 2 different batteries from the bunch I have. They are fairly new. I drained the battery down to 7.0V, then placed it into the charger. The charger puts out 20ma charge current. The charger claims it takes 16hrs. Explain to me how in 4 hours the charging was complete? The battery voltage was 9.85v when the charging was done, which sounds correct. What happened to 16hrs? I verified the charge current of 20ma, and charge voltage of 11.65V. I also drained another fully charged 9v battery with a 40ma draw. In just over 1hr the battery dropped to 7.0v. I tried charging that battery, and in 4 hrs that was also charged. I'd like to know how only 20ma in 4 hours charged a 300mah 9v battery. What did they do, lie about the mah rating?

  2. doug08

    Thread Starter Member

    Jan 30, 2011
    I'll have to ask this question in a forum which specializes in rechargeable batteries.
  3. bertus


    Apr 5, 2008
  4. Tealc


    Jun 30, 2011
    Aren't most 9v NiMH batteries actually only 7.2v by virtue of using 6 cells of 1.2v? I know some are 8.4v and some are 9.6v. Which have you got?
  5. iONic

    AAC Fanatic!

    Nov 16, 2007
    What makes you believe the batteries are fully charged, the charger or the battery voltage. If the batteries you have are either the 8.4V or 9.6V type they were not fully charged. In the case of the 8.4V(nominal) measuring 9.85V removed from the charger may indicate a full charge.

    Ideally, It would help to know what battery chemistry you are talking about as well as what the nominal voltage is...7.2V, 8.4V, or 9.6V. Also what charger you are using and does it indicate when the battery is charged. I myself would not discharge the batteries less than 1.1V/cell, meaning 6.6V for the c cell battery, 7.7V for the 7 cell battery and 8.8V for the 9.6V battery if they are either NiCad or NiMH. Technically they should charge up to 9V(6 cell), 10.5V(7 cell) and nearly 12V(8 cell).
    Last edited: Sep 27, 2011