mixing battery in a battery pack

Discussion in 'General Electronics Chat' started by mrel, Jan 25, 2010.

  1. mrel

    Thread Starter Senior Member

    Jan 20, 2009
    I have Ryobi 18 volts battery pack found 3 bad sub -c battery in the pack.
    The battery don't have any marking say if it is a nickel -cadmium or nickel metal hydride battery,
    Since I don't know what kind of battery is in the pack ,if I were to mix in the pack with nickel -cadmium and nickel metal hydride battery, will battery pack work,take a charge?:
    There is total 15 sub-c @ 1.2 volts battery in the pack connected in series .
    Since only 3 battery is bad I hate to buy all new battery.
    There is two issue one don't know what kind battery in the pack,second issue is can I mix two different type battery in the pack ( nickel -cadmium and nickel metal hydride battery together)
    Thank for the help
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    The lesser batteries will steal charge from the new batteries. You should replace all.
  3. Darren Holdstock

    Active Member

    Feb 10, 2009
    Yup, don't mix 'em. Even if they were all NiMH cells the differing characteristics would mean they wouldn't charge properly, and the weaker cells could be damaged during discharge in use. NiMH and NiCd definitely don't mix.

    You could try reconditioning the rogue cells with a few charge/discharge* cycles, assuming all the original cells are the same type, just in different states of repair. Use an NiMH charger - this will charge both these and NiCd types (not at the same time though!), whereas a NiCd charger won't charge NiMH properly or safely.

    * Don't discharge the battery pack below 1 V per cell to prevent "cell reversal", or discharge each cell individually. NiMH cells won't tolerate frequent deep discharges, but will benefit from the occasional deep cycle.
  4. hgmjr

    Retired Moderator

    Jan 28, 2005
    I too would advise against mixing NiCad and NiMH batteries. The charging profile for these to batteries are substantially different. If you are interested, you can go to www.batteryuniversity.com and find out more about the differences in the charging strategies for these two different battery technologies.