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Thread: Your experiences, rechargable batteries. NiMh vs NiCd

  1. #1 Your experiences, rechargable batteries. NiMh vs NiCd 
    Forum Isotope (In)Sanity's Avatar
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    So I've been doing some interesting testing lately with my NiCd, NiHm peak charger (really made for my model plane). I had two sets of NiCd batteries for my cordless drill that I was going to trash as the original charger refused to put a drop of power in them (Would last 5 minutes). So I know this Peak charger I've got is an ok unit for charging NiCd's and NiMh (has a switch) batteries I figured what did I have to loose by charging the cordless drill packs with this charger.

    The peak charger works by detecting the voltage drop at the peak of charge. In other words the batteries will ramp up in voltage during charge and then have a dive once they are fully charged. This device detects that and helps keep them from being overcharged.

    So I charged these rather lame 9.6 volt NiCd packs up at 2 amps and now have working batteries where before I had nothing (close to zero volts out of the packs).

    So anyone have experiences with NiCd or NiMh batteries they would like to share. Does anyone know what exactly happens to the internal chemistry of a battery by so called overcharging? I've heard you should not leave NiMh batteries on the charger as they will "overcharge" even at low currents.


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    Forum Masters Degree invert_nexus's Avatar
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    Is it possible that it has to do with battery memory? I remember having a problem with the battery of a forklift once and the tech that came out to service talked about how if the battery was charged before it was fully drained that it would affect the memory of the battery and over time the battery would hold less and less charge. The solution to this is to completely drain the battery dead and the recharge it. I believe it was referred to as 'topping it off'. It was a long time ago and I forget the specifics.

    Of course, forklift batteries are a bit more complicated than a cordless drill battery. But, I've heard this same type of advice given on other rechargeable batteries. That to ensure the longest life of the battery, one should fully discharge the battery before recharging it.

    So. Maybe your charger does this?


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    Forum Isotope (In)Sanity's Avatar
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    Yes, actually NiCd batteries "memory" effect from what I've read can be fixed by allowing the cells to discharge way down <1 volt per cell and then fully charging them again. This sometimes has to be repeated a few times to recover the cells. NiMh cells on the other hand do not suffer from this problem. They do however from what I've read so far suffer from "overcharging". I'm still trying to figure out exactly what this so called overcharging does to the battery. I've also read that NiMh cells don't like a lot of heat, but it's common for them to get over 130F during a fast charge and that this heat is normal.

    In the event of my dead cordless battery packs I suspect the stock charger could not charge them back up once they fell to such a complete total discharge. The peak charger I used is adjustable for different charge rates and I think was able to handle the totally dead batteries. Now I just need to cycle them a few time to get them back up to snuff. They will never be brand new, but at least they last a whole lot longer then 5 minutes. They also have far more overall power in terms of torque with the drill.

    I don't know, just an interesting subject at the moment for me. I like to be an expert (or sound like one) for these day to day life household products.

    Ohh side note, pretty much everything I've read says that overcharging NiMh batteries kills them. So the cheap chargers that are more or less just timers will do them in pretty quick. So, as always you get what you pay for and pay for what you get.
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    Forum Sophomore Elbethil's Avatar
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    I used NiCd batteries for a long time (about ten years), then my charger sorta died.

    I tried using rechargable Alkaline batteries. They exploded in their charger after their fifth recharge. I gave up.

    I started using NiMh a month ago and have been pleased with them. I've only had to recharge my two NiMh batteries once since their purchase.
    "In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move." -- Douglas Adams
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