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Thread: is there a formula for life of a battery mah vs ohm?

  1. #1
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    Question is there a formula for life of a battery mah vs ohm?

    Im just curious if there's a formula I can follow for ammount of mah vs ohms of my atty and battery life. Lr attys kill my battery a lot faster but there's gotta be some kind of simple math I can do to predict how many batteries I need to bring with me when I travel. Any insight?
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  2. #2
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    I don't use a formula, just figure out how many batts you go through in a day, and add 1 to that for 'just in case'.
    I would have to get smarter just to be dumb.

  3. #3
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    I ask because I am trying to finger out a good ohm to mah ratio for me. I know a lr atty will sucker punch a battery and reduce its charged life to about half I imagine but there's gotta be a way to figure out exactly how much.
    Cattle die, kindred die, Every man is mortal:
    But I know one thing that never dies,
    The glory of the great dead

    Only a slave avenges himself at once;
    and only a coward never.

    Roughstack v2
    Ego passthrough 750mah
    ego t passthrough 900mah

    --------------------------------

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  4. #4
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    due to the fact that mAh ratings are not all created equal and are very often misrepresented there is no simple math formula.

    different types of batteries are rated under different load levels. standard li-ion batteries will have a higher mAH rating than IMR batteries of the same size but they will run dead quicker than the IMR batteries. this is because the Li-Ion batteries had their mAh rating calculated under a lighter load than the IMR batteries.

    this is just round numbers to keep things simple.

    suppose a Li-Ion battery has a 1000 mAH rating based on a 1 amp draw.

    the same size IMR battery has an 800 mAh rating but it is based on a 1.5 amp draw.

    now you use that battery on an atty that is drawing 1.5 amps.

    your result will be a true 800 mAh rating on the IMR battery but the Li-Ion battery that is being used at a higher draw rate than it was tested under is only going to work as a 750 mAh battery.

    bottom line the forumula you are looking for is experience + use = knowing how long a battery will last you with the equipment that you use.
    06-20-2009, 01:59 AM EST (The moment it all began)

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  5. #5
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    The formula you are looking for as a general guideline is,
    A=V/Ω and T=mAh/mA.

    Say you use a 2600 mAh 3.7V battery and 2Ω atty, you will pull about 1.85 amps or 1850 milliamps.

    2600/1850=1.4 hours of on time.

    Use a 1000 mAh battery, and the same current draw; you get .54 hours of on time.

    Use a 180 mAh battery and the same current draw; you get .097 hours of on time.


    Of course all of this is curved and way more complex than the simple outline above; the voltage changes over the charge of the battery so your amps will start high, then go lower as the battery discharges. But as a general guideline it ought to help.
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  6. #6
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    Quote Originally Posted by Jaguar View Post
    Of course all of this is curved and way more complex than the simple outline above; the voltage changes over the charge of the battery so your amps will start high, then go lower as the battery discharges. But as a general guideline it ought to help.
    So, in other, less wordy words....

    Quote Originally Posted by Coop View Post
    just figure out how many batts you go through in a day, and add 1 to that for 'just in case'.
    and

    Quote Originally Posted by dumwaldo View Post
    bottom line the forumula you are looking for is experience + use = knowing how long a battery will last you with the equipment that you use.
    I would have to get smarter just to be dumb.

  7. #7
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    Double the OHMS = Double the life ! = 1/2 the current draw

    so higher ohms give longer batt life .

    Batts store CURRENT so less draw = longer charge time

  8. #8
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    Quote Originally Posted by Coop View Post
    So, in other, less wordy words....



    and
    Yeah, or that.
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  9. #9
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    Yeah but your math looks nicer.
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  10. #10
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    Quote Originally Posted by Jaguar View Post
    The formula you are looking for as a general guideline is,
    A=V/Ω and T=mAh/mA.

    Say you use a 2600 mAh 3.7V battery and 2Ω atty, you will pull about 1.85 amps or 1850 milliamps.

    2600/1850=1.4 hours of on time.

    Use a 1000 mAh battery, and the same current draw; you get .54 hours of on time.

    Use a 180 mAh battery and the same current draw; you get .097 hours of on time.


    Of course all of this is curved and way more complex than the simple outline above; the voltage changes over the charge of the battery so your amps will start high, then go lower as the battery discharges. But as a general guideline it ought to help.
    I am not trying to be obtuse, just making sure my own BASIC understanding of things is somewhat accurate but doesn't all that fancy math fail to take into account the C rating for the battery that was used to come up with the mAh rating for the battery. As I understand it Li-Ion batteries are rated at a lower Amp draw than IMR batteries and that is the reason for the large discrepancy in mAh ratings for batteries of identical size.
    06-20-2009, 01:59 AM EST (The moment it all began)

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