How can I discharge NIMH battery safely?

By erwin1978
Sep 1, 2003
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  1. I'm trying to get the most out of my NIMH batteries by discharging them completely. One of the cells has more charge than the others so I want to make sure this particular cell has the same charge as the others before I recharge them. Is it safe to short the batteries by directly connecting the +/- terminals together with a wire? I figured I would discharge them to 0 volts or close to it.

    I don't know much about the specs of my charger so I don't know how it determines the batteries are fully charged. I do find that one of the batteries gets hotter than the others so I figured it might be overcharging this particular cell while the others aren't getting fully recharged.

    I wish I had a Maha C401FS charger. That thing charges 4 batteries independent of each other so even though the batteries have different charges, the charger will only recharge each of them until they are full.
  2. StormBringer

    StormBringer TS Maniac Posts: 2,244

    You can buy chargers that will fully discharge batteries before it starts charging them. Or you can connect something to the battery to discharge it. I wouldn't recommend simply shorting it. The best way to do this would be to use a small light bulb or a coil or something that will serve as a load to discharge the battery without creating a dead short, else you run a moderate risk of causing a problem with the battery, the least of which might be current leakage, or possibly causing the battery to explode.
  3. Nic

    Nic TechSpot Paladin Posts: 1,549

    NiMH batteries don't suffer from the 'memory' effect that NiCd batteries are prone to. You don't need to discharge NiMH batteries for them to be at their best, and in fact fully discharging them may damage the cells. If the cells aren't holding equal charge, then maybe your battery is reaching the end of its life. If you are getting a decent run time when fully charged, then they are probably fine. Ignore trying to discharge them, as you won't gain anything by doing this.

    Something you could try is to put your battery into the freezer overnight, then remove it and let it come back to room temperature. This 'trick' can apparently help to break up any crystals that form in each cell and so help to revitalise poor performing cells. Let us know if this works, as I've never tried it myself. :)

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