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What is the typical mAh capacity of a 9v?

Discussion in 'Power Electronics' started by Protoman, May 21, 2021.

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  1. Protoman

    Protoman

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    Dec 30, 2020
    Over the past few months I was tinkering around with some small home made projects (following youtube videos mostly) and I've gone through a lot of 9v batteries during that. One thing I noticed in experimenting with batteries is that while obviously alkaline are superior to carbon-zinc. When it comes to AA, AAA, C, and D cell batteries, a carbon-zinc will power it up just fine (just for not as long, obviously). But when it comes to 9v applications, I've seen some stuff that will not power up even when a fresh carbon-zinc 9v is used.

    That being said, due to the cash I've sunk into buying 9vs, I want to buy a few rechargeable ones. I saw some on Aliexpress that make me wonder if they are for real or not. Specifically this one:

    https://bit.ly/3oMdCjD

    It's a pricey one for sure, but... 6800mAh? I read that your average Alkaline 9v has a capacity of around 600 or so mAh. Is this for real? Because if it is, I wouldn't mind ordering a pair as it'll be the only 9vs I'll ever need. but I'm very skeptical.
     
  2. Bluejets

    Bluejets

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    999
    Oct 5, 2014
    The standard 9v smoke alarm battery has a capacity of around 260mAh BUT........ as with all batteries the mAh rating depends on the discharge rate.
    It could be 1,5,10 or 20 hr discharge time.

    Batteryuniversity web site should have details of the discharge time versus capacity charts.

    Anything advertised anywhere with unrealistic capacity values are more likely than not, crap.
    Case in point would be the range of 18650 cells one sees on Ebay and the like.
    Some will go as high as 9000mAh which is again, as above.

    If you tell us your application, we can possibly point you in the right direction as how to go about it.
    Do you specifically require 9v for example and what loading.??
     
    dave9 likes this.
  3. Audioguru

    Audioguru

    3,238
    702
    Sep 24, 2016
    The size and weight of that "6800mAh" 9V battery say it is only 600mAh to 1200mAh like all the others.
    The No-Name-Brand others also might be lying about their capacity.
     

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  4. Bluejets

    Bluejets

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    Oct 5, 2014
    EBL for example on Amazon, show a discharge curve with volts and amps but no time base so pretty useless .
    Just put there to try to impress I'd say.
     

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  5. Protoman

    Protoman

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    Dec 30, 2020
    I figured. If anything sounds too good to be true, it probably is.

    EDIT: I also need to finish going through the whole battery university thing. It's fascinating.
     
    Last edited: May 21, 2021
  6. dave9

    dave9

    1,078
    292
    Mar 5, 2017
    While that 6800mAH is fraudulently rated, any with Li-Ion cells are likely to use the funny Chinese math where the tell you the capacity of the 3.7V Li-Ion cells, not the output at near 9V.

    I'd only use the rechargeable 9V battery in an existing product that requires that form factor to fit in the battery bay, not some project where you can decide on something else, with the exception being a portable headamp, where the smaller size in your pocket means everything, but these days kids just drive cans from their phone or bluetooth buds and live with the result.

    What the best solution is has a lot to do with your desired maintenance recharge interval, budget, and acceptable size increase. If you have a standard cylindrical cell bay, Li-Ion charger then I'd sooner go with 14500 cells or 18650 if a pair is not too big for the application, or otherwise, depends on what your circuit's max and min voltage tolerance is. Minimum tolerance tells a lot about how much useful capacity you'll get out of any particular battery config.

    However, if the circuit uses so little current that the 9V batteries in question are capable at all, then I'd look at using one of those SMPS boost circuits on ebay, aliexpress, etc for around $1 each, then pick which cell chemistry, size and # of cells fits the project best.

    If you don't have a Li-Ion cell charger but do have a NiMH charger (if you don't have a NiMH charger, do get one, is is obscene what it costs to always run alkalines) then perhaps 2x AA cells along with the boost circuit mentioned previously, although it would be more efficient with 4 x AA or AAA than 2x.

    Here are some examples of the boost boards but read through their described specs to see if they fit the need. There are several more on ebay alone, and they're cheaper in bulk if you might have use for more than one.

    https://www.ebay.com/itm/353495103215
    https://www.ebay.com/itm/353406412315
    https://www.ebay.com/itm/402850501612
     
  7. Bluejets

    Bluejets

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    999
    Oct 5, 2014
  8. Martaine2005

    Martaine2005

    3,408
    926
    May 12, 2015
    Why don't you buy a cheap bench power supply or use surplus wall warts/adapters?
    The bench PSU should have current and voltage adjustment.
    And with a multimeter, you can test/check the current required for the DUT and use suitable batteries for long term use.
    Exactly!
    Most homes have plenty of surplus mains adapters. Typically 5V, 9V and 12V are in every home.

    Martin
     
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