Pager batteries - NiMh vs Alkaline

Discussion in 'General Electronics Chat' started by chrischrischris, Nov 7, 2015.

  1. chrischrischris

    Thread Starter Member

    Feb 18, 2012
    283
    10
    Hi.
    I'm wondering if someone can please help me with this query.

    I'm a member of a CFA in Australia and we have around 10,000 member in the state. Each of us carry a pager that runs on a single AA battery. We are issued with Duracell Alkaline batteries. These last around 3 to 4 weeks, hence that's alot of land fill.

    I've debated with our CFA headquarters about considering the use of rechargeable batteries (namely NiMh, 2550mAh, AA's). I'm told that only "Duracell AA, Alkaline" batteries are recommended. Why? Who knows!

    I've personally been using rechargeable batteries for about a year now. They last about the same time - 3 to 4 (maybe just a couple of days less). I also seem to receive all emergency calls (when checking with other volunteers).

    I know that the Alkaline AAs start at around 1.64V and the NiMh I have start around 1.44V. At about 1.25(?)V, the pager beeps every couple of hours as a warning that the battery is getting low (with either battery). At around 1.22V, the pager turns off (again with either battery). Between the warning to "off" seems to range between 4 to 7 days (depending no. of calls received).

    Plotting the discharge of both batteries, I found from full to empty, the Alkaline is quite linear. The NiMh however seems to drop quite quickly to a low value, but then holds this value for a long time.

    My questions are:
    1. Is there "any" possibility that reception would be worse with one battery as compared to the other? (I haven't found this to be the case)
    2. If the answer to the above is "no", what "facts" can I forward to my brigade in defense of the suggested change.

    Any facts, web links, literature, etc, would be kindly appreciated. Thanks in advance.
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. MrSoftware

    Active Member

    Oct 29, 2013
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    You're in a different country so maybe (hopefully?) it's different there, but here in the US when you can't find a logical reason for something like this, start following the money trail. Is the pager manufacturer, or anyone along the supply chain associated with Duracell in any way? Maybe they have a marketing campaign together, or maybe the pager maker gets a break on battery prices to recommend Duracell brand? etc.. There very well could be a technical reason they're recommending only Alkaline batteries, but recommending a specific brand makes me think there's just as much business reason as there might be technical reason.
     
  4. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    You correctly discovered that alkaline batteries hold a slightly higher voltage than a rechargeable battery. That can make all the difference in performance for a low current device designed for 1.5 volts instead of being designed for 1.2 volts. On the other hand, my cheap flash camera works exceedingly well with NiMH batteries instead of alkaline because of the intermittent heavy current used to charge the flash device. Your experience in real life testing trumps any guesses from several thousand miles away. ("One real test result is worth a dozen theories.")

    Now that you have proven that NiMH batteries are about equal in your application, I would suggest you carry an alkaline battery for a spare because they have a very good shelf life.
     
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  5. Roderick Young

    Member

    Feb 22, 2015
    408
    168
    This is more an issue of the model of pager than the battery, in my experience. I haven't carried a pager for almost 15 years, as cell phones have supplanted them, but I remember the issue you described on early pagers. The last one that I had, contained a setting for battery type, and you could choose NiCd (NiMH) or Alkaline. I would get good life from a NiMH in that case. So take a good look at the settings. If your pagers are starting to detect low battery at 1.22 volts, as you've noted, a NiMH reaches that quickly.

    Perhaps 20 years ago, I recall one FRS communicator (like a walkie-talkie) for which battery voltage DID matter for range. The NiMH lasted longer, but didn't have the same reach in distance. All you can do is experiment with that sort of thing. I didn't believe it myself at first.
     
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  6. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    I would think that battery voltage would likely have more effect on transmitter power (such as in a walkie-talkie) then a receiver (such as a in a pager) sensitivity.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Nickel chemistry cells have a nominal 1.2V, alkaline are nominally 1.5V - almost 1.6V when fresh.

    Some devices won't work properly on the lower terminal voltage - if at all.

    Also; nickel chemistry has a reputation for self discharge over time. You can buy low self discharge types - but the ones I bought left me disinclined to recommend them - YMMV.
     
  8. chrischrischris

    Thread Starter Member

    Feb 18, 2012
    283
    10
    Thanks Bertus
    Nice link for battery info, unfortunately didn't have exactly what I was after.
    MrSoftware
    I tend to agree. It "feels like" our CFA, pager supplier and Duracell have a sweet deal going on because I can't support their reasons.
    AAC Fanatic
    I absolutely agree on carrying an Alkaline as a spare.
    Roderick
    I think looking at my first tests (see below) I was wrong about the minimum voltage before the pager turns off - I think it's actually around 1.150V.
    Crutschow
    Yes, this is what I think. This pager is simply a receiver, not a transmitter.

    My "guess" and please let me know if you agree or disagree. The CFA I believe has either had these pagers programmed by the supplier or programmed themselves the "workable" operating voltages. I think that the maximum it will accept is around 1.65V as I once tried to fit in a battery I used for a camera that was around that value and it wouldn't turn on.

    As mentioned earlier, the pager "beeps" once every few hours or so, once it drops to 1.25V. I believe this has been programmed to beep at this level to warn the CFA member to replace the battery soon. At around 1.15V (sorry 1.2V I mentioned earlier was wrong), the pager just switches off.

    What this means I think is that the CFA intends for the pager to still work between 1.25V and 1.15V. We have never been told it will not operate between those values correctly - i.e. not receive "all" emergency calls.

    I "believe" that it were able to drop below 1.15V, only then would the signal probably be compromised. But the pager has been set to turn off at that value, so we wouldn't get into that situation. What do you think?

    (note, I'm doing another more control test between the 2 batteries now, however below you can see that infact the Alkaline lasted 29 days up to when it "beeped" and the NiMh's 22 days for one and 26 days for the other.

    [​IMG]
     
    Last edited: Nov 12, 2015
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