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  1. #1
    RC Qualifier
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    how to tell mah of a battery

    Aquired a couple used lipos. one is a 2s and one is a 3s .

    I understand that IF they were 5000 mah it would be okay to charge at 5amp.

    The labels are gone, I dont know what they are. I have been charging at 2amp to be safe, they look bigger than that.

    Any way to tell what they are?

  2. #2
    RC Champion trax de max's Avatar
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    A quick guess would be to put the packs at storage level, then charge up. When it's full check how much mA went into the pack, then double that figure.
    So say you managed to put in 2500mA from storage(50%) to full(100%), double that figure and it will be a 5000mAh pack.
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  3. #3
    RC Racer
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    Perhaps I'm confused; I'd thought:

    Storage *voltage* is 3.8-3.85v. That's what a battery should be stored at.

    The MAH that you can put into a battery that's storage charged is typically more than 1/2 the total it can hold, so I don't know that doubling it is a good rule of thumb.

  4. #4
    RC Turnbuckle Jr.
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    Storage *voltage* is 3.8-3.85v. That's what a battery should be stored at.
    Yes... that's 50% of being fully charged (4.2v). "Dead" (or as low as you should really go safely) is 3.4v.

    Another way to do it is to just run it until LiPo cut off in your car... then put it on the charger and fully charge it. Any decent charger will display how many Mah it put into it.

    What kind of charger do you have?

  5. #5
    RC Racer
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    The "charge from empty" is a better test than the "charge from 3.8v" test, IMHO. At least that gives you some idea of what size of battery you have, even if the battery isn't fully discharged (so in reality your battery is a bit bigger than this test would show.)

    I have a Powerlab 8.

  6. #6
    RC Champion trax de max's Avatar
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    As long as you know what empty is.
    From storage to full, just take it to the next full amp Lower on charge, eg. 2600mah into pack, instead of 5.2A just use 5A as the charge rate.
    If the traxxas packs are capable of 2C then you could even use upto 10A and be within specs.
    Last edited by trax de max; 06-28-2015 at 03:49 PM.
    Google search trumps Wiki. Refer to user guide.

  7. #7
    RC Racer
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    I just don't think that at 3.85 you're at 50% of power. I think you're under that.

    Here's what I did:
    1. Took a 4000 mah 3S battery into storage charge, 3.86 per Powerlab 8.
    2. Charged it at 10 amps to full:

    a. At 4.06 --- 870 mah added
    b. At 4.11 --- 1100 mah added
    c. At 4.15 --- 1300 mah added
    d. At 4.18 --- 1375 mah added
    e. At 4.20 --- 1712 mah added

    Ok, so this is a pretty good test.

  8. #8
    RC Qualifier Panamon Creel's Avatar
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    yeah agree, storage voltage is 50% of the conservative LiPo voltage range but that does not equal 50% of the capacity, also since those LiPos are used they'll likely have a steeper fall-off and reduced capacity to begin with.

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