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Analysis of rechargeable batteries

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  • Analysis of rechargeable batteries

    I selected two types of NiMH rechargeable batteries to test. First I tested Eneloops, a very popular low self-discharge battery. Then I tested Sanyo 2700 mAh batteries, one of the highest-capacity reliable rechargeable AA batteries available. Eneloop batteries weigh 26 grams and the 2700 mAh batteries weigh 30 grams.

    I conditioned new batteries and charged them in a Sanyo NC-MDR02NU charger. This is the best compact, lightweight, reliable charger I could find that works on interational voltage rates (100 to 240 volts). It weighs 76 grams. It charges two fully discharged batteries in slightly less than 4 hours.


    Eneloop batteries lasted 19 hours and 22 minutes, and the 2700 mAh batteries lasted 25 hours in the Dakota 20 using the same test methods I used for alkaline and lithium batteries. The 2700 mAh batteries are obviously superior when using the GPS for a long time, but if you're just using it for short periods of time followed by long periods of disuse, the Eneloops would be a better choice since they don't lose much charge while not being used.

    Next comes the weight savings analysis. Which battery will save weight on a hike, disposable lithium or rechargeable NiMH? This depends on two things: the total legth of the hike, which dictates how many disposable batteries would be needed, and the maximum amount of time between opportunities to recharge batteries, which dictates how many rechargeable batteries would be needed. In general, longer hikes with more opportunities for recharging favor using rechargeable batteries, and shorter hikes with less opportunities for recharging favor disposable batteries. The following table summarizes the results. I used 10 hours per day of hiking time.

    Code:
    Weight with charger    Recharge frequency  Lithium equivalent
    —————————————————————  ——————————————————  ————————————————————————————————
    2 batteries 136 grams   25 hours,  2 days  10 batteries, 150 hours, 15 days
    4 batteries 196 grams   50 hours,  5 days  14 batteries, 210 hours, 21 days
    6 batteries 256 grams   75 hours,  7 days  18 batteries, 270 hours, 27 days
    8 batteries 316 grams  100 hours, 10 days  22 batteries, 330 hours, 33 days
    But there's another consideration. The load gets lighter as time passes with disposable batteries but not with rechargeable, so the average load with lithium batteries is one-half of the amount you start with. With this in mind, here is a chart using average weight instead of starting weight for lithium batteries.

    Code:
    Weight with charger    Recharge frequency  Lithium equivalent
    —————————————————————  ——————————————————  ————————————————————————————————
    2 batteries 136 grams   25 hours,  2 days  20 batteries, 300 hours, 30 days
    4 batteries 196 grams   50 hours,  5 days  28 batteries, 420 hours, 42 days
    6 batteries 256 grams   75 hours,  7 days  36 batteries, 540 hours, 54 days
    8 batteries 316 grams  100 hours, 10 days  44 batteries, 660 hours, 66 days
    The next consideration is reliability. Chargers can fail. And although battery failures are unlikely, they are not impossible. If one of your disposable batteries should fail, it's probably not a big deal. But if one of your rechargeable batteries fails, it could make a difference.

    Disposable batteries are simpler to use because you won't have to change batteries as frequently and you don't have to worry about remembering to recharge your batteries at night and making sure not to forget the charger in the morning!

    One more point I should mention is that lithium batteries don't lose as much power in cold weather as NiMH batteries do.

    In sumary, assuming weight savings are your first priority (true for me), I think I would only want to use rechargeable batteries when it's a really long hike and I am sure I will be able to charge the batteries at least once every two days. For any long hike on the Great Wall I don't think rechargeable batteries are appropriate. If cost savings is more important to you than weight savings, rechargeable batteries are a viable choice for a long hike. I hope this analysis will help you to decide when to use which type.

    Of course, the weight savings analysis assumes you won't be able to buy lithium batteries during your hike, which would be true on the Great Wall but not so, for example, on the Appalachian Trail.

    My next step will be analysis of solar chargers...
    Bryan

  • #2
    Re: Analysis of rechargeable batteries

    Very interesting review. I'm looking forward to see your view on the solar charges.

    I have been able to use Lithium the whole way on the Great Wall. In minus 10C to 20C they had a noticable drop in performance, but otherwise very good. I have kept some of the batteries that stopped working in extreme heat, and plan to test them when it is warm to see how much juice they actually had left.
    Robert -

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    • #3
      Re: Analysis of rechargeable batteries

      Very very interesting again !

      We have the same point of view concerning NiMH. I'm planning to use eight 2700 NiMH battery with a charger for a thru hike of 40 days approximately.

      In France, I have more experience with GP PowerBank (see http://www.gppowerbank.fr/) but not tested with Dakota yet. Have a look, it seems one of a lightweight charger can charge four 2700 NiMH in the same time than your charger (but yours it's only two 2700 NiMH).

      For me, solar chargers to charge NiMH battery with efficiency look like very heavy. But of course, I'm waiting for your test which will be very interesting !

      Many Thanks again

      Comment


      • #4
        Re: Analysis of rechargeable batteries

        Actually I have a doubt in flooded lead acid battery. So I wanna ask one question. These flooded batteries are using in electric vehicle. When we did high speed testing, that time suddenly negative battery terminal melts. Why is it happened in negative terminal? and why not in positive terminal? I have seen four batteries, in all the batteries negative terminal only melts any specific reason is there. If anyone knows please clarify me.

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        • #5
          Re: Analysis of rechargeable batteries

          This discussion has nothing to do with car batteries.
          Bryan

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