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Rechargable Batteries

Discussion in 'Techie Discussion' started by Shovel, Jan 11, 2004.

  1. Shovel

    Shovel Can't get enough of FH

    A quickie:

    I use quite a few AA recharable batteries at the moment, since they're cheaper to maintain for portable CD players and so forth.

    However, the ones that came with my charger (Ni-Cd I think) completely die if left unused for a period of time. Is this normal? Can you recommend something else? The charger will support Ni-MH as well (which I use in my Logitech MX700 and work lovely from what I've found).

    Thanks
     
  2. Big G

    Big G Has a sexy sister. I am also a Bodhi wannabee.

    A quickie reply:

    Right, i know about this in a wishy washy way - so forgive me, but I think it's something to do with battery memory.

    Infact, here's a website about it all http://www.zbattery.com/zbattery/memoryeffect.html

    There is no point in me relaying into a post. Hope this helps!!

    Edit - also, rechargable batteries do die altogether and stop holding their charge. My electric shaver battery will only last a whole day fully charged. Additionally, the battery for my 8210 phone only lasts about 2 days (should last five) after a full charge. They do "rot" after a while and don't last forever.

    G
     
  3. Whipped

    Whipped Part of the furniture

    Yep, my old Palm V was left discharged for about a month and now I have to dismantle it with the aid of a hairdryer (no screws, superglue) to replace it :(
     
  4. Tom

    Tom FH is my second home

    Memory effect is a bit of a myth. What happens is that over time, each cell becomes inbalanced when compared to the other cells around it, so you end up with a situation where a 9V battery, containing 4 1.5V cells, fully charged, only has 8V. This is because 1 of the cells instead of being at 1.5V, would be at 0.5V. When the battery discharges, that cell, instead of dropping to 0V, goes down to -1V. This effectively helps to discharge the other cells, and battery life is further reduced.

    The batteries that I use for work are computer controlled, and can be revitalised (ie each cell charged individually to eliminate the imbalance), but its expensive technology. It still happens even with Nickel Metal Hydride, or Lithium Ion batteries.

    What you should consider is the lowest voltage a piece of equipment will work at. For instance, a device might operate on a nominal voltage of 12V, but work fine down to 10.5V. The battery you use to power it might provide useable current from 12V down to 9.5V, so obviously you're not getting the full use of the battery once its voltage drops below 10.5V. We use batteries that fully charged at at 13.2V or even 14.4V, this way, when the batteries are nearly discharged, their voltage is still above the minimum voltage that the equipment requires, and you get 100% of the use of the battery.

    You should also consider the fact that rechargeable batteries do not normally work well in cold temperatures, particularly Nicads, which if charged below freezing, can actually become explosive.

    Anyway, yes, it is perfectly normal for Nicads to discharge over time.
     
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